Get >= 2 A*s. This will outweigh your relatively poor GCSE grades. What're you A levels in? I'm assuming Biology, Chemistry plus at least one of your remaining two in a rigorous subject..
Be more careful with your choices - why did you choose these 4? Did you assume they'd be easier options? You can tailor your choices after you do the UKCAT again. I know that I only got interviewed for KCL in the first batch of applicants because of my UKCAT score.
Improve your UKCAT. How much prep did you do before the UKCAT? Did you use the 400 questions book? The VR score will probably be the easiest to improve, but even if you do improve your VR score to the average of the other 3 sections (643) you'll still have a fairly mediocre score. So, if you want to be in the first round of applications considered you're going to need to work hard on all your sections.
You've got an extra year to beef up your experience c.f. other applicants, so medical schools will expect you to have used this year wisely. Long-term experience will be key, ideally paid. HCA work would be excellent.