-Any guides to Eliot which might be useful
There's a lot of good guides to Eliot out there (to name a few, there's that 15 dollar Waste Land app on iTunes, bookrags is amazing (definitely get a class subscription to this, if you all want to chip in ~80 cents), poetry.rapgenius.com was surprisingly useful for disentangling his transliterary fetish, there's a lot of informative youtube videos on the context and function of his poetry, and as if you needed to be told, sparknotes is always there) but I never really found any of these especially useful in SAC tasks. Your own impression of Eliot will constitue the bulk of your writings on him, if not the whole, so just read and re-read. Your understanding of his poems, of course, will feed your demonstrable knowledge, but please, please do not become dependant on studyguides.
-Ideas on HOW to tackle and analyse the lexicon of his poetry
Not too sure what you mean by lexicon, but in analysing a poem - any poem - the big thing you have to do is
correctly link technique to function. A lot of people (or at least, most low-scoring essays and students that I see) mistakenly suppose that the non-prosaic nature of poetry can be exploited to draw out any kind of interpretation from any technique they happen to identify - linking said technique to a function it may not necessarily serve. For instance, saying that Eliot's use of enjambment in the opening lines of The Waste Land emphasises the sense of loss in post World War I Europe may
sound right, when in fact it's pure bullshit, as enjambment just draws attention to whatever words or moments are enjambed, and so you can't draw the previous reading out of those lines alone.
Anyway, the only thing you need to worry about when analysing Eliot is making sure you have some level of original analytical exposure to all of his prescribed poems, and ensuring that you don't fuck up when describing the role of poetic technique in his creation of meaning.
-Examples of essays/poetry analysis
Most example essays worth reading cost money, but the second I can be stuffed transcribing my SACs onto word, I'll post a couple of Eliot essays in the sample compilation thread.
Oh, and good luck! Don't listen to the naysayers who get frustrated with him, Eliot is amazing and beautiful and
don't do him for your creative response!