heads up nl seems to be my strongest game, far stronger for me than rings or shorthand, since i find it much easier to pick up patterns in peoples play when i only have to concentrate on one player. some thoughts:

i wouldn't agree that you should never check or call from the small blind. sometimes you can win big hands by checking a monster like AA or KK from the small blind. especially on the internet, people wont' put you on these hands, and if you let them drive the betting, sometimes they can pay you off..

mixing up your play is very important. so you should sometimes raise with junk hands like 36off, and sometimes raise with AK. basically, when you're heads up, throw the mathematical rule book out the window. since you can win your opponent's whole stack on one hand, its more important to deceive him with your play, rather than play mathematicallly correctly. you want him to misread you and push all in when you hit a monster flop or have preflop nuts.. ie AA KK.

playing AA, KK, QQ, AK heads up:
in ring and shorthand, raising with these hands is usually a must, however heads up, i usually play these hands differently. in a 3 or 4 way pot, one usually overbets the pot on the flop to shut out draws (provided you hit with AK). however heads up, there is less of a danger of getting outdrawn since you're only against one opponent. if the flop isn't dangerous, your strategy should be to TRAP with AA or KK, QQ less so. this all comes down to your judgement however since your opponent may actually have something.. again this depends on your reads. but i've done many de-stacking plays by calling AA from the small blind, calling all the way to the river and putting them all in. it helps if you've pulled a couple of big bets they've folded to in previous hands.. (increases the chances they will think you're bluffing!)

hand values:
hand values have to be modified for heads up play. suited connectors are mostly junk unless they're quite high like j10, 109 even. i do think stuff like Q10 offsuit is actually playable most of the time heads up. this is because heads up, people raise with all kinds of junk like 34off. hands with any ace or king are quite strong too, because if your opponents cards are unpaired, there is a 2/3 chance you are winning at the flop with ace high, even if you don't pair your hole cards. however i don't trap or slowplay with ace high hands like i do with AA or KK because these hands DO get outdrawn heads up. so raise the hands and bet them strong on the flop, and be prepared to lay them down for any show of resistance.

blind defense:
you should usually defend your blinds against a raise heads up. sometimes it pays to just fold, not just because you have a shit hand, but because sometimes you should just fold to mix up your play. however most of the time, if the raise is small, you should see a cheap flop. why? there is a roughly 1/3 chance that you will pair either of your hole cards on the flop, and if you do, there is a very high likelihood that you are winning at the flop. however against a tight player who doesn't raise very much, you should fold, because he probably has a sick hand. also (as applies to everything heads up) don't bet predictably, ie always betting the flop when you hit any pair, since this will allow your opponent to pick up your betting pattern and trap you when he flops his top pair or set.