Does anyone have any advice on how to get the most euphoria out of stimulants?

Rail more stims.

If they are of the amphetamine family then taking antacids and drinking water throughout can hugely increase the duration and gives a higher peak, especially if you are taking them orally. MAOI's will inhibit the metabolism of many types of drugs (phenethylamines), however this can be suicidal because they make your dose equivalent to a MUCH larger dose. Trying new fun activities also has a very powerful effect (music, excersize, masterbation/sex have been the greatest for me).