Activations, activations, activations. Turn 1 will probably be mostly stalling, hit-n-run popups and staying out of sight. Don't be too tempted to over extend falcons to get some shots off on a double leaving them open to retaliation - even a BM is useful against guard - he will fail some activations. (eldar are vulnerable to this too incidentally, all the more reason to hide). Failing makes him take the tough choice of using the reroll or saving it in case the tanks fail. Sentinels shouldnt worry you, they cant do much, are fragile and this gives you forward targets to break to reduce his activation count (as Dave says try to do it before they activate, he will end up having to activate something important that can't see anything, or waste them on 100 point scouts). Plus you can take rangers (where are your rangers?) which are just as cheap and more durable can take cover and not vulnerable to AT). So I would concentrate on the smaller things first rather than piling in on the tanks straight away. Bear in mind how expensive those tanks are and what they'd have to kill to earn their points back. Terrain can make them less effective than it might appear.
It can be good to get used to counting remaining activations on both sides and working out if you have enough of an advantage to move unopposed at the end of the turn. You will need this at some point as it will require a combination of formations to eventually take down the BTS - you want to stack as many modifiers on the assault resolution so that more die, hence it must be prepped with BMs and preferably a couple of casualties - it takes 4 hits on average to kill a russ, but each kill in assault can kill another in resolution, so combining that with lance and macro hits in assault can have a multiplying effect that shooting just cannot achieve. Likewise, once broken, BMs will decimate them much more efficiently than regular shooting - good thing you've got disrupt that can hit anywhere on the board then.
If you're worried about artillery (especially if he uses manticores instead of bombards, which cannot reach your deployment zone) then break them with the void spinner. Artillery can really wreck your day.
Against guard it is more achievable than many other armies to set up a rolling assault for turn 2 or 3 (assault, consolidate, retain, assault, consolidate, retain, assault). If you pull it off you'll feel like a gaming god
If you lose initiative then you're toast. Most opponents won't allow it to happen but it can be fun trying!
