We rarely do anything flawlessly. Many things need to be trained before you can make these flawless and so also declutter. We are all different and we learn from different things. Some avoid mistakes to the last while others never seem to learn from their mistakes. No matter what type you are, we can state that it is human to make mistakes and most people actually learn from their mistakes.
Mistakes I made during my declutter time 20 years ago when I started decluttering, I didn't know where to dispose of the things I cleared out. Back then, second hand was not as big as it is today. The mistake I then made was that I threw the things in the bin. In fact, they are the only thing I regret about my declutter all these years. Pretty incredible considering I've been doing this for 20 years. So with that being said, I would advise you to dispose of the things you purge properly. Different countries have different ways of sorting what you declutter, so find out where your things go when you're done with them.
Other common mistakes A common mistake that people often make is that they buy boxes to store and organize things in before they have even started to declutter. If you don't know how much to declutter, how can you know how many boxes you need to buy. Buying these before you declutter is like bringing more unnecessary things into your home. Declutter first and organize later. Sorting can be done in cheap moving boxes, bags or boxes you already have at home.
It is thought that decluttering is a one-time thing. Oh how many times I have seen on Youtube when people say that I should do a big declutter once and then I will never do it again. Wrong. We bring things into our homes all the time, boxes that the cereal is in, the plastic bag that the cheese comes in, new clothes for the kids, shoes that break and so on. No matter what, you will always need to continue to declutter throughout your life. The goal is for you to declutter so much that you only need to maintain the home after that. But as long as we bring something into the home, something also needs to go out. Think about how the body works, a little like the home works too.
Another common mistake is that people overwhelm themselves by thinking they can do everything in a short period of time. It took you time to accumulate everything and it will take time for you to get rid of everything. Most people are attached to their things and have a hard time decluttering them. It is completely natural. Declutter is like learning to ride a bike. First you have to practice and practice but then the declutter muscles build up and you will get better and better at it.
An extension of the above point. Don't push forward more than you can handle to avoid stress and locking yourself up. It's easy to get overwhelmed when you see all the things. I strongly recommend that you collect your things in categories and do the whole category at the same time, but sometimes you don't have the opportunity to do that if the category is too big. Then it's better to go drawer by drawer, cabinet by cabinet and when you feel it's manageable then collect all of the same and declutter the entire category at once. By category I mean all your books, all your clothes, everything in the kitchen and so on.
Never start with your sentimental things. It includes photos. Starting with your sentimental stuff is like asking for things to go bad. If we are attached to a broken t-shirt how attached are we to the card grandma wrote before she passed away. Never start with your sentimental things because it is a failure. Start with what you are least attached to and that is individual. Many say start with the clothes, but many are also incredibly attached to their clothes. Take what feels most right for you. I personally recommend the kitchen items or the litter box because these are usually the areas where we are least attached to things. Bathroom products are also a good thing because there you can often just throw away empty or old packaging and it immediately looks much better inside.
Regardless of how you choose to start, avoid the mistakes most people make anyway. Start small with something you feel least attached to and realize that this will take time and you will need to declutter in layers upon layers. Eventually you will realize that you should not bring in as much as you usually do, it will come naturally with time. You become more aware of what you buy when you have gone through your entire home and examined everything you own. Think of it as the goal of purging is not only to get you the life you dream of, but also to have touched every single thing you own and that way you have more control over your own home. You will know exactly where every little thing is when you go through the home and declutter what you no longer need, use or love. Good luck.