The 3 Greatest Lessons I've Learned After 25 Years in Business and $100 Million in Revenue Here are the three most valuable lessons I've learned over 25 years of business ups and downs.

In June, I reached a milestone with my business, PostcardMania: 25 years in business. It got me thinking about all the lessons I've learned as a business owner and entrepreneur.

Starting out, I was greener than green. There have been hard times when I didn't know what I was doing, but I've made it from nothing to $97 million in annual revenue, over 350 staff, and we're still growing — averaging 20% revenue growth over the last three years after a year of growing at a much slower rate of 5% in the decade previous.

Through those experiences, I grew as an entrepreneur and gained valuable business insights, but I sure wish I had someone to confide in at the time.

I want you to avoid some of the missteps I made on my journey, so I've taken some time to nail down the three greatest lessons I've learned over 25 years of business ups and downs — thankfully many, many more ups than downs.

Related: 10 Lessons I Learned as Someone Who Has Spent 10 Years Running a Business

Lesson #1: Your marketing budget and revenue growth are tied together

There have been times in my career that I've had the choice to either pay myself or pay for marketing. In 1998, I was a graphic designer with a dream and a computer — and that's about it!

When I started PostcardMania, I put as much of my money as possible into marketing. I barely paid myself a living wage for years because I was so determined to grow my business.

I drove an old Nissan Pathfinder to save on a car payment. I used credit cards to help pay for things at times (although you should definitely avoid getting into debt if you can) and even took money out of my own home to purchase a building for PostcardMania (this was a hugely smart move for me and worked out great).

Those sacrifices paid off when my business took off. The more I marketed, the more leads came in, and the more my revenue skyrocketed. As PostcardMania achieved steady growth, I increased my marketing budget too. I noticed that my revenue increases mirrored the amount I invested in marketing. The more money I put into marketing, the more money we made.

Think of it like the classic board game Monopoly. At first, you feel hesitant to spend the $1,500 you start out with in the game (I didn't even have that to start with in real life!). But you quickly find out there are two types of players: the ones who hoard their money to try to play it safe and the ones who spend all of it on properties — and now I have enough money to actually invest in real estate, and I have a lot of that now too.

Eventually, everyone realizes that the players with the most properties win because every time someone lands on that space, they get cash.

It's the same in the real world. If you don't spend as much money as you can on marketing, someone else will — and your business will pay for it in the long run. But if you're the one marketing, over time, you'll get that money back and then some.

So, buy Park Place … and New York Avenue. Then, once you get some more cash from those, put houses on them. You get the picture: The biggest winners don't play it safe. They make moves all over the board.

Maybe you aren't currently spending any money on marketing and need to set a budget. Take the time to sit down and create a marketing budget ASAP, because it's your first step to success.

Related: 7 Business Takeaways You Can Learn From Monopoly

Lesson #2: You need a unique selling proposition to beat your competition

A unique selling proposition or USP is a one-of-a-kind aspect of your business that none of your competitors have. Take Zappos, for example. Tony Hsieh started one of the first online-based shoe retailers, but even back then, he had competition.

What set him apart? Free shipping on all returns and exchanges. He realized that what prevented people from purchasing shoes online instead of inside a store was not being able to try them on before a purchase. By eliminating the issue of spending money on returns, people could buy as many shoes as they liked without worry and just return the pairs that didn't work without financial penalty. Zappos sold to Amazon for just shy of a billion dollars in 2009.

When I started PostcardMania, we set ourselves apart from the competition by being first at a lot of things — the first to sell direct mail postcards directly to businesses for really low prices, for example, rather than paying $1200 for 5,000, we sold them for $329 for 5,000; the first to offer free marketing advice without charging a retainer, including having a blog before the word was coined; and the first to offer every service needed, from order placement to postcard delivery, under one roof. We didn't have just one USP, we had several!

Those first years in business were a rocket ride to eight figures. In just four years, we rode an industry disruptor's wave to over $10 million in annual revenue. We were growing close to 100% year after year.

But my competitors caught on. They quickly started doing the things we were doing, and the effect on our bottom line was unsettling.

I knew I had to do something, so I took inspiration from Zappos and Tony Hsieh.

I looked for something within my industry that people hated and which could prevent them from buying — and I found out it was the fear of not getting a return on their investment. People wanted to know they'd get results from mailing postcards, so I addressed the issue head-on. I hired a full-time person (which has today turned into an entire department) to track the results of our successful campaigns and figure out which factors contributed to that success.

Today, we have thousands of successes analyzed and over 750 case studies published on our website (we only publish with permission) where clients can view exactly what businesses in similar industries did to bring in revenue. None of my competitors do that!

So, take some time to sit down and define what makes your brand unique. Be sure to go deeper than just claiming to have "the best customer service" or "the best product." Then market it like crazy, and watch the results come in.

Related: 4 Critical Business Lessons I've Learned as a CEO

Lesson #3: Create an integrated sales funnel to generate a better return on investment

When marketing your business, you need a whole arsenal of tactics. When those tactics work in harmony to move a prospective buyer from unaware to aware to interested to purchasing, it's called a sales funnel. An optimized sales funnel integrates online and offline technology.

A game-changer for me was when I added digital advertising to our direct mail campaigns. We knew we had to stay ahead by investing in the latest technology, and that meant digital targeting features and website integration.

Postcards in the mailbox were no longer just postcards in the mailbox — they became launching points for people to connect with a brand online. Mail pieces at home, ads on your social media feeds, brand reminders on the videos you watch and at the top of your inbox, it all works together to feed traffic to your website, where the real magic can happen.

Whether a prospect enters a sales funnel with a mailer or a click on a website, the key is always follow-up. Every action your prospect takes should prompt them to take another action that brings them closer to buying. Once a prospect progresses far enough along your funnel that they visit your website, you want them to fill out a form, email you, call you or even make a purchase if your site has an ecommerce system.

Too many business owners look at this first website visit as the be-all-end-all in that prospect's customer journey. But one of the biggest lessons I've learned in my 25 years is to never give up on a lead — and I do mean never.

For example, if a prospect visits your site but doesn't convert, you can still follow up with them offline through a technology called direct mail retargeting. It works like digital retargeting ads but uses physical mailers instead to encourage them to return to your website or make a purchase. These mailers are automated, so you don't even have to lift a finger to launch the process.

Related: 21 Lessons I Swear By After 21 Years as an Entrepreneur

Never underestimate the power of tangible advertisements. That's why direct mail has been such a powerful marketing tool for me — it allows the recipient to touch, feel and see more than the typical digital ad.

Keep in mind that it can take time for people to take action, so stay consistent with your follow-up. I continue to email, call, mail to and display ads to every prospect that has ever visited my website and converted, regardless of time or inactivity. My sales funnel is on constant repeat until someone asks to be removed because I would rather be a little bit annoying to a few leads that I can remove than repeatedly miss out on the day someone else is ready to buy.

Last year, I actually looked into whether emailing old leads was worth it. I asked my email specialist a couple of years ago to compare our sales logs with our email habits and the age of certain leads. Over the course of June and the first two weeks into July, 782 leads that were 3+ years old responded to our emails, and 53 of them placed new orders. Over the same period, 526 leads that were 5+ years old responded and 29 of them placed new orders — and summer is our slowest season. That's 82 new clients over the course of just 6 weeks that I would've missed out on if I didn't follow up with every lead every day.

So, even if it seems daunting to start, keep at it, closely track your results, and stick to what works. It took time for me to learn how to build a sales funnel that generates over $80 million.

Lastly, remember that experience is always the greatest teacher. Keep trying different marketing techniques, and you'll find your own truths as well. I'm sure I'll learn even more over the next 25 years of owning a business. The lessons never stop.