For vocab, get used to looking words up in your dictionary as well as learning common words.
Mr Masterman made lists of these most common words (or in fact 3 lists..), which I collated into this list
http://quizlet.com/7681558/mastermans-entire-tough-flash-cards/ Quizlet is really handy for learning words; after you finish a set, you do it again with only the words that you got incorrect. great tool for any Vocab/formula/definition memorisation work that you may have.
also, it can be printed out in a table format, which has the Latin (or whatever) on the left hand side, with the translation on the right. you can then fold the sheet down the middle and then it makes a nice double sided card (Latin on one side, English on the other) which is great for learning words.
Don't be scared though of not having a huge vocab. In the exam, you need to be absolutely sure of the meaning of the word, so you may well end up looking for words that you do know but aren't certain of.
For this reason, I probably consulted Mr Dictionary for about 20 words from the unseen.
More important I think is to know grammar really well, and to be able to recognise what sort of word it is (eg is that an adjective, noun or a verb participle) and so then you are able to look up that word in your dictionary quickly and without too much hassle.
Also I'd recommend reading the Aeneid, at least an abridged/concise version of it (doesn't need to be all of it in translation), in preparation for the essay section of the exam. you need to have a general understanding of the Aeneid as a whole, and this is the only real way to get this understanding.
good luck. should be one of your more enjoyable subjects