Every year during tax season, I regret not keeping my trading records well in advance. My assumption is: you can't remember every trade in your head, so aim for "reproducibility" as your goal. At the very least, store records of deposits/withdrawals, the transaction prices and fees for each currency exchange, and the txid of on-chain transfers. Ideally, organize them into folders by wallet address and exchange account. Don't just save screenshots; too many screenshots are a disaster. Export CSV files with notes on what you were doing at the time—this can be lifesaving at the end of the year.

Recently, everyone has been watching large on-chain transfers and the movements of hot and cold wallets as "smart money." I do that too, but I also casually record these transfers. Otherwise, when explaining the source and destination of funds later, I won't be able to clarify. Anyway, my current principle is: it's better to spend an extra two minutes organizing now than to leave the pain until the end of the year.