There are a number of good strategies for preventing amphetaminergic neurotoxicity:
(1) Use regular d-amphetamine, instead of the more neurotoxic methamphetamine and MDA/MDMA (anything with a methylenedioxy substituent is going to produce more oxidative stress).
(2) Keep your dosage reasonable--don't use massive tweak-a-thon binge doses. Also, always take your amphetamines orally as they were meant to be taken, that way you get a nice, smooth stimulation without a sudden massive jump in plasma concentration.
(3) Ensure that your core body temperature stays as low as possible--neurotoxicity is directly linked to hyperthermia, so chill out (literally). You can use a little paracetamol (a little) with a NSAID to lower a fever if it occurs.
(4) For anti-oxidant supplements, try Vitamins C, D and E, as well as resveratrol. Levo-deprenyl is also good, but keep your dose low if you are taking it with amphetamine. Ergoloids like hydergine work too.
(5) Throw in a little magnesium to lower amphetamine tolerance.