If I want to become a Clinical Psychologist, what can I do early on in order to get my foot in the door?
There is no "foot in the door" process of becoming a clinical psychologist. You must obtain either a PhD or a PsyD to become a clinician AND pass a national licensing examination to practice.
It's not clear to me how long you have been out of school since obtaining your BA (or BS) in psychology. Since graduate programs are highly competitive, I would recommend going for a masters degree and then attempting admission to a doctoral program. You will need research experience, strong letters of recommendation from faculty members and very high GRE scores. This is the reason I recommend starting off with a masters program so that you can gain research experience and establish relationships with faculty members who are in a position to write those letters of recommendation.