If you want to use meth and do something other than hump the side of your bed for 3 days, then you need a routine. A proper routine will keep you healthier than many non-users, as well as ensuring that the drug never has total control of you.
6:00AM - 12:00PM: Eat breakfast before you dose. An apple, muesli bar, glass of milk and some nuts goes a long way. Take your supplements: Creatine 7.5mg, Magnesium citrate 2000mg, Fish oil 4000mg. Keep your hygiene in check. Shower, brush your teeth, shave, cut your nails, moisturise. If you pick your face often, make sure to do this before you dose. Then dose — swallowing it in a capsule is the least harmful route. The only way to prevent neurotransmitter toxicity is to not take too much.
12:00PM - 12:00AM: Work towards a goal. This is the absolute most important step in not devolving into a tweaker. If you don't have a goal, then you don't have a sensible reason to do meth. Stay frosty — don't exercise, don't stay out in the sun, suck on ice. Sip water slowly. Chew xylitol gum.
12:00AM - 6:00AM: Eat dinner with lots of protein. Brush your teeth. Take an antipsychotic like Seroquel to ensure sleep. If you did everything correctly, you should fall asleep within 30 minutes. Getting into a regular sleep pattern is insanely important when you're speeding, and the shadow people will always remind you of that.
A routine like this will allow you to use meth in the context of a functional, normal lifestyle. When used to achieve real-world goals, you'll be fully in control and will have few health complications.