I find it can be quite stimulating for the lady to fit the condom and that always helps ;-)
make sure there is lube on the cock.. it increases sensitivity. ....
otherwise guys should wank with a condom on. It teaches them how to get and stay hard.
But not down to the base or the condom will slip off. Obviously or maybe not........
Sometimes... condoms have to be a good fit. Guys have different size willies. If a guy has a bigger than average one, or a fatter than average one, the condom can be too tight and that can cause loss of erection. This is easily solved with the use of larger condoms.