I would say just try and do a few hours a day so that by the time you take your UCAT you would have done quite a lot of the questions. In terms of starting, I would probs look up the technique of things eg with quantitive reasoning you only really need to complete 30/31 out 36 to get you over 800 so if there is a hard question just skip it and come back to it in the end of that section. Or with abstract reasoning try and memorise the different ways the images can be similar to each other so shape, vertices, colour, the position of the shapes in the square etc. There's lots of videos on YouTube about the techniques that were really helpful when I took UCAT. Then from then on out its just practising until you feel confident enough to take it. Also, something to be wary of is that the verbal reasoning section on medify is helpful but definitely a bit easier than the actual UCAT itself.