Before someone decides to shoot me down I have checked erowid and UTSE on this site and my questions still aren't answered.
Me and a few friends are considering trying amphetamine this weekend, first time for all of us - I'd like to know how much to take and the most advanced ROA. I know most will say start small and work up but I'd prefer a numerical figure, one I can work from
Thank you for your time, Sprout
People generally don't try just "amphetamine". Most of the time you take drugs that are metabolized into amphetamine, contain a mixture of amphetamine salts, racemic amphetamine, isomers, other things. Adderall is a well known example of a group of amphetamine salts, it's mostly made up of dextroamphetamine, which is right isomer of racemic amphetamine. Adderall contains racemic (pure) amphetamine as well, and levoamphetamine, which is less psychoactive but more stimulating.
A common mistake is confusing methamphetamine, and other ***-amphetamine drugs as amphetamine itself, when they're actually separate drugs with seperate isomers but are built from amphetamine. Ritalin, if you get that, is actually a completely different structured chemical which is more like cocaine than amphetamines.
The reason Erowid, if you go to their page for, say, Adderall, lists it as "amphetamine" is that there are so many mixtures, combinations, formulas, salts, and other amphetamine-related things it's easier to just put it all under one. You'll notice seperate pages for methamphetamine and others, though, as they are chemically seperate.
By ROA I assume you mean route of administration, here's my view of the routes, the doses, the difference in come up, peak, intensity of crash, etc. I'm using Adderall IR Generic as the example here.
20mg is a good starting dose for a first timer for recreational effects, taken orally. Come up is 30-60m depending on stomach contents, it peaks around that time, and lasts for ~2-3 maybe 4hrs after, you may be hungry but food might taste horrible. An acidic stomach will lessen the effectiveness when you take it orally, even a can of soda will make the effects less and last shorter. If you piss a lot, that's a sign it's leaving your body quicker. You'll feel peaceful inside, feel motivated to do things, feel a rush, feel happy, social, content with your life. Might be twitchy, maybe a little over stimulated, just read erowid like you are. Might feel 20mg is too much. You may hate this drug outright too, I prefer downers recreationally myself but amphetamines are the perfect thing for a day you can't deal with.
Insufflation, 10-15mg. For 15 cut the pill in half (
assuming 20mg pill, dont tell me it wasn't enough and you actually had a 5mg, check the imprint on RXlist or something), then take one half and cut that in half. Take either the one leftover half and one of the 1/4ths, crush it up (I like putting my pills in a spoon then crushing them with another pressed down on top when I rail them) and read some insufflation guide on BL. ~10m come up, maybe an hour of effects more intense than oral, the time really depends, quick, hard crash which will leave you wanting more. Much more euphoric than oral.
Parachuting- 15mg, use the method above but dump the powder into some toilet paper and swallow it all. Bit quicker come up, short effects, maybe a little more intense and about the same crash as oral.
Plugging- 10mg, shove a 10mg pill up your ass. I really couldn't tell you what to expect from this as I've never done it before (don't trust it works

).
Also, don't overdo it, don't do it at nighttime, don't go looking for special things to enjoy like doing random shit while you're stoned. The high isn't like that- it just enhances everything so it's more enjoyable or tolerable with some degree of euphoria. Reading, typing, fast paced music, being social are the best on this. Video games can be fun too, building yourself up to be smart and superior to everyone around you is also a whole lot of fun, as is fucking with people in chat rooms. It's definitely NOT a "chill and watch TV" thing. That's a total waste. Enjoy it while it lasts though, it's your Adderall IQ and remember it's only temporary omnipotence

.
And of course, have fun!