WK, a couple of things I've discovered is that you can have two records beat matched nicely, perfectly if you will

Now, when it comes time to drop record B into the mix and it is very noticably not beat matched all of a sudden. I believe the reason for this is because your dealing with an analogue device and as a result the surface of the vinyl A is going to alter to *some* degree, hence the platter is still revolving at the same speed 33/45rpm but the record because of its contour and friction is going to throw your beat matching estimate. Doesnt happen all the time, but it does happen.
Personally, I've found it helpfull to familiarise yourself with the feel of the vinyl on the platter as your beat matching with it. If its relatively flat or slightly concave its going to be more prone to being manipulated from the inner ring with a slight push. If its slightly convex then your a brave man (or desperate

if you touch it there. I've found twisting the nipple (or alternatively pinching it, to slow the platter) of the deck to be very handy if things are drifting slightly. I'm opposed to using *just* pitchbending because it doesnt rectify a mistake for me as quick as possible. But thats just my milage, yours will differ.
Another thing I find helpfull when I'm mixing is, say for example you've got track A and B again. Track A is playing away which is primarily composed of drums. Your starting to mix track B which has a trancey/keyboardy thing going on with it. I'll always manipulate the track with the drums as if you have to slow down or speed up the trancey bit, people are going to notice it and laugh at you
Ideally you should invest as much time as you can in mixing two tracks. Use as much as track A as possible, as opposed to swiging on a beer or trying to smoke a bowl

so you've got the best advantage when it comes time for everyone to hear the mix. Use your eq's too, they're there to get you out shit
Just play around with it, everyone has there own 'style' it'll come to you with plenty of practice.