My mistakes in crypto investing are:
1. I used small exchange that was hacked, and I haven't withdrawn funds on first signs of trouble.
2. I bought mostly shitcoins when I started to be interested in crypto. Almost all of these projects are now dead projects or practically worthless.
After having these bad experiences I sold almost all altcoins (for very low price) and have almost exclusively BTC, and try to keep my funds on exchanges for very limited time.
Those actually are very basic mistakes we all make. At the initial stage, we would not really chose a reputable exchange but will chose convenience. If we find some local exchange offering faster withdrawals/deposits at the moment, we would prefer investing with that exchange instead of looking for the reputable ones. It is only when we face a situation like this, we realise how big mistake we made and now recovering those funds is almost next to impossible. That's why choosing the right exchange is the first and foremost step while trading or even investing.
It is understandable why you chose shitcoins at that time. I am sure you might have seen the huge upside potential because a few of these shitcoins have actually performed quite well in the past. Hope you learnt from your mistake. If yes, I'm sure you would never go that path again.