I will begin this question with the following disclaimer:
I am absolutely terrible at RTS games.
With that in mind, I am hoping that a simple, general strategy may be proposed for a noob player that really does not want to get deeply involved in learning the ins and outs of each class...I do not plan on going through the single player or learning enough to professionally compete, this is more knowledge for the person who will play this game a few times within the course of the year.
That being said, I am going to be doing some LAN gaming soon and this is one of the games we will play. The last time we played I got absolutely creamed and would like to at least put up a decent fight.
I have no race preference...really whatever is the easiest to get up and running and put on a good showing is what I would prefer. We have all of the expansions, so the extra races are available as well.
I think the general rule of one strategy per answer would be appropriate here as well.