Watching replays is great but the only way to play a race is just to play it yourself. Lose a few times, and see what you did wrong
edit: each time you play, play with a different stragety in mind, and see which ones worked and which ones doesn't. My recommendation is to play the same map with the same AI every time. Perferably if you don't want to start again, save the very beginning and name it differently say if you start of with an large map and this time you want to aggressive, save it as largeagressivegame1 and then every time you save for aggressive name it largeaggressivegame1.2 or something like that
edit1.2: it might also help to include the number of ai and the type of ai in the game save name also
edit2: and don't just play one race, play each of the races, know it strengths, weakness, where in the research are they a superpower, for example in tech they are are a economic superpower, you get the point.
