I can't remember which is which for more than five minutes!

I don't have a problem actually conjugating and don't have any tricks for it.

It comes with vocabulary. Once you have a vocabulary that contains enough verbs to hit all the cases, the rest just land in one of the cases by example.

If you know 泳ぐ (oyogu) very well, then even though you don't use 仰ぐ (aogu) very much, you just conjugate it intuitively like oyogu.

When you're speaking, there isn't enough time to go through a roster of rules.