Hi Dani
I did my AST test in August and I am currently waiting for my medical to go through. I am 31 & struggled at the beginning as I've been out of school for a few years.
I would say the most important thing is to use the revision booklet and practice the tests in there, also look at the GCSE bitesize website, the mechanical and electrical section we do not need to pass but I would say you still need to revise because it helps towards ur overall mark.
Also if u can time or get people to time u because I found that helped. Also I found the Memory test part was one letter came up on the screen at a time and not a list like the practice booklet and then u need to remember the letter in between.
The maths and english were not too hard I know it sounds pants but take a watch in and I left it on my desk and roughly timed so I could pace myself. Maths I paniced and thought it would be hard but it was just the type of questions in the practice booklet, also maybe read an article of a newspaper and then get someone to test u on what u have read.
I hope this helps if u would like any more information or help, please pm me and I would be more than happy to help as I have had a lot of the help along the way as well, everyone on here has answered any questions I have had.