I'm also a PPL student (although in Prestwick...)
For most people theory is self study. Get the text books (a few options - I went for Pratt) and learn the material - don't just cram to pass the exams as almost all of it is practically useful in some shape or fashion. I haven't had any problems with the material - but I haven't taken any exams yet (it is up to the training organisation whether you need to take air law before you solo).
The more often you can have lessons the better, as you will forget things less and so need fewer revision lessons. Lessons are often not long, as certainly when doing circuits the workload is so high you will be brain dead after not much more than 30 mins! Weather is an issue in the UK, so the more flexibility you have the better (some people only seem to fly 1/2 of their booked lessons). In saying that though, I've had very few lessons as "wash outs" as my instructor has been able to find something to do not too far from the airfield that doesn't require no cloud. At this time of the year in Scotland, light is an issue as sunset is pretty early (so can't fly after work).
If you're learning in a club rather than a training organisation, you might get the opportunity to sit in the back of other's lessons. This can sometimes be as beneficial as paying for your own.
Aircraft wise, I'm learning in a Scottish Aviation Bulldog, but I started my training in a Bolkow Junior. I've also had a lesson in a PA28 Cherokee. Primarily you are learning to be a pilot, not an operator of a particular aircraft, so although they are three very different planes, I was able to move between them fairly easily (although it does mean I've had a few lessons which were just to get used to the new aircraft). As has been mentioned above, this shouldn't be your primary worry (although if an organisation has multiple of the same type it is an advantage as all planes need regular maintenance).
Enjoy!
(and in case you haven't read other threads -
don't pay up front 
)