The size of your dimension text is between you, your company, and your clients, but generally it will be somewhere between 3/32" and 3/16" when printed. I personally like to place my dimension while working in the scaled viewport, and let AutoCAD automatically scale the dimension relative to the viewport scale so it will aways print the size I specify without ever having to set or change dimension scales. You'll probably get different advice from others, so I recommend you try each method and print them out so see which suites you best.
Here's a related topic that pretty much covers all the different options. I posted a screenshot of the method I use in post #32 http://www.cadtutor.net/forum/showth...782#post356782