First, almost all schools require two semesters of grades, they'll usually get your transcripts mid-summer and make decisions from there. There are a few exceptions to this rule - GULC/WUSTL will let you apply with only one semester's worth of grades, for example.
A compelling reason to transfer will probably help you more than anything else; unfortunately, these often include things that you can't "work on," such as transferring to be closer to where you're from originally or to be with a spouse. My impression is that any other reason to transfer won't hurt you (it IS almost all about the grades, after all), but it won't boost your chances.
One affirmative thing that you can do once you're in school is to participate in class and go to office hours so that you can differentiate yourself from the 100 or so other students in your section. Ideally, this will lead to a good letter of recommendation as opposed to a lukewarm, more generic one.