Oxford & Imperial CS Gap year

I've got an offer from UCL CS but I'll probably have to do a gap year due to the new Student Visa ban. Expecting to get 3A* achieved in A Levels

I'm also planning on doing A Level FM during my gap year, and I'll probably get predicted A/A*, and then I'll apply to Oxford & Imperial since I have FM now (Didn't apply before since I didn't do FM). And apply again to UCL and some other unis

Anyways, what else can I do during my gap year other than Working to improve my personal statement and maximise my chances for Oxford & Imperial?

And when would you recommend I start studying for the TMUA if I'm aiming for a 6.5-7? My A Levels end on June 18th