hmm
Nice reply... kinda off topic
Well for the tips. I play starcraft too! (Dark-MOJO)
ok here goes. In custom, the computer always rushes, so build some defence. you can easily win from the comp if you get lotsa strong units first, and then totally seal off your base (turrets, bunkers etc) so the comp cannot enter
In Multi, this strat is worthless, good players always manage to destroy your defence. So always build OFFENSIVE units instead of DEFENSIVE units. If there is no rush time, always rush. Or you can build units, upgrade and defend yer town with those units while u r building better units. In a 20 nr game, build lotsa strong units before attacking. ALWAYS get more than 1 active building (Unit producing building) so you have a faster buildup.
You can check the official strategy site too:
http://www.battle.net/scc/
Good Luck