When I read over my material after writing it, I always find errors or parts that could be made better. every time. It's never perfect, and that’s just from my point of view. When you write a published adventure, you are writing for a lot of different people who all have different ways of looking at things and different approaches to solving problems. I believe the more you can accommodate that diversity, the more successful your product will be. How do you do that? In a word, playtesting.
Playtesting serves several functions. It gives you an idea of how well balanced the encounter combats are, it helps you gauge how interesting your plot is, it helps you realize plot holes you may have not thought of when writing the adventure and it gives you access to a database of bright ideas if you are willing to listen.
You should have several rounds of playtesting. Your first round, or alpha playtest, should be with close friends. This is important because you want honest feedback, and your close friends are usually the ones who will be brutally honest with you. These folks are your inner circle. Once you’ve run it through with them and made the changes needed, and there will be changes, you can start reaching out to the community. This is your beta playtest. Your product should be pretty much complete at this point. Now you are just tweaking a few things here and there. In the beta playtest, you might find out that an encounter is too strong for a non-optimized party or that another encounter is needed to accommodate an unrealized adventuring direction that the characters might take. Going outside your inner circle for the beta playtest is important because these are people who may have a different play style than what you are used to, and you want that change in perspective.
Once you have finished your alpha and a couple of beta playtests, you are ready to have someone else run the adventure for you. This is probably the most important playtest of all. This playtest is to ensure your product is both readable and that it flows the way you intended. You should do a couple with you as a player and have a couple done without you in even in the same room. The first one or two with you as a player are important because you need to be there to answer questions. You should also be writing those questions down, so you can address them when you revisit the adventure. Oh, it should be a different group with a different DM each time too. Once the other person runs the adventure and you aren’t having to make clarifications or answer unknowns, you can have someone run the adventure without you around. When those playtests run smoothly, then your adventure is ready for the public.