Domain trading is generally a long term game, I wouldn't recommend doing anything sub 1 year.

Best tactic I've seen for it is to buy something up, set it up as a proxy site to create traffic through it via proxy.org then let it run. By the end of that period the general usage it's had and age increases it's value significantly. You need a significant number of domains to make any money out of it though and ultimately it comes down to whether or not people will ever want to buy the domains from you, without demand what you have is worth nothing anyway.