Hey Dark Seraph -

Definately don't do coke. Such a loser drug. Other than that, I don't really have too many tips for you because it depends on the individual person as opposed to the masses. What I mean is, motivation comes differently to everybody.

I'm not any kind of motivation-ologist or anything but here is what I do if I find myself getting lazy-

1. Smoke pot a little less often
2. Get into a regular exercise routine
3. Find a buddy who will play sports with you (in your case, tennis)
4. If you eat crap for munchies, cut that out. I always feel like shit after about a thousand Chee-tos, but if I eat a fruit salad after smoking I don't feel like such a slug.
5. Here's the best tip of all - don't let it get the best of you! You have to create your own motivation - I don't know you well enough to know what would get you up off your ass, only you, family, and good friends know that much.

6. Do as I say, not as I do. (I can be one lazy MFer sometimes, esp. in Winter)

Hope this helps even a little, and take it easy bro.

-DB