Im on dexamp as a ADHD medication and tolerance do develop rather quickly but it drops very fast too which is why I think that "mypassports" advice about taking some days off every now and then is the best thing that you can do in order to keep tolerance down.
I have been on this drug for about a year now and my dose is actually lower now than it was a year ago.
I started on 15 mg a day (3x5 mg) but found it to be way too much so I jumped down to 10 mg (2x5 mg)
I did a lot of experimenting with dosing so that I could figure out what would be just right for me and one of the things I found was that Im much better of taking just one dose a day when comparing positive effects to the side effects so now I do 5 or 7,5 mg a day unless I need a longer coverage, in which case I will take 2 x 5 mg.
Point being, that I will encourage you to mess around with the dosing untill you find out what works the best for you.
Next step will be to keep your tolerance on a level where the choosen dose remains effective.
In order for it to remain effective, you are going to need some days off. How often, I dont know, but speaking from experience, I can say that I have 1-3 (1-2 most of the time) days off a week and tolerance seems to be very close to baseline.
It should be noted that Im also taking 600 mg Magnesium citrate a day, for multiple reasons, one being that it decreases tolerance development.
This is due to its NMDA receptor antagonism and is therefore not exclusive to Magnesium.
You should read up on the relationship between NMDA antagonism and amphetamins, I think you will find that part usefull.