Honestly you'll probably be fine, I was the same as you before I started, worried about falling short of the year 1 requirements. However I hadn't done any maths or science since GCSEs (5 years ago) and even then they were all foundation tier papers, so very basic content. You've got A-level maths so that will take a lot of pressure off you, plus the mechanics modules will help with physics.
As for tips, I'd say to make sure you attend all your seminars and lectures. For physics, make sure you do the recommended reading before the lecture, even if it is just a brief scan over it the morning before the lecture, it will mean you actually understand what the lecture is talking about and means you can take notes. That way you can use lectures more like revision classes. I didn't do hardly any recommended reading in second semester and struggled to concentrate in lectures as I had no idea what the lecturer was talking about so it bored the hell out of me just sitting listening to nonsense.
Take advantage of free periods between classes, obviously make time for lunch or whatever, but if you have got a free period hit the library and go over material covered in a lecture or do the reading for another lecture coming up.
If you are studying in private and get stuck, write everything you get stuck on down on a sheet of paper, so next time you are in the seminar, your professor can explain it to you.
Also there are some pretty useful revision tips in the following link
http://www.southampton.ac.uk/edusupport/ldc/docs/Memory%20revision%20and%20exam%20techniques%202009.pdfJust make sure you understand the vast majority the content covered by the end of each week.