For example: Scizor https://pokemondb.net/pokedex/scizor
Pre-evolution moves these moved will be learn/relearn only by pre-evolution (Scyther), and cannot learn/relearn when you have Scizor. So if you check and see that the move in list pre-evolution moves not need for your moveset at the end. You will not worry for evolution or not. However, if the moves have in that list, you will need learn/relearn it before you decide to evolution to Scizor. We have relearner NPC for help you relearn moves [based on the moves learn by level up list] at cerulean, safforn, goldenrod, blackthorn, lateport and sootopolis.
As a result, thinking about moveset carefully and then you will know what you need to do. About evolution soon or latter, I will recommend often keep it and evolution only at around level 97-98 for avoiding bug/unexpected happen. Pokemon evolution already will need more exp than pokemon pre-evolution.