DIY bike tools?

I've never used one of those things. I use needle nose pliers (or my hand) to pull the cable tight and hold the brake arm in, and then tighten the screw with my free hand. There's a hozan you can get for like $22 shipped on ebay, but I've always been too cheap.
 
Try pulling the cable tight, using a small vice grip clamp the cable so it cant slip, then tighten. What are you doing just adjusting your breaks? If so it just takes a little practice, but all you need is the proper size wrench. Look up how to tighten breaks. I think doing derailers is trickier, I usally pull it a little tighter than I would actually want, but when its all tight its right where I want. It is truly just all in the feel and that just takes practice to gain.