well, first of all consider I haven't won a competitive match as of 2014 and my only win is a friendly against Tonga (close match btw) so I'm not sure I can be of much help with this...
defensive tactics are recommended, low tempo and time wasting strategies might help keeping scoreline relatively low.
counter attacking football is hard to implement as you'd need pacey wingers/strikers for that, while the average SM player is quite slow (you might be lucky and already have quick regens though)
I was quite happy with a very defensive 5-1-3-1, felt we were doing a good overall job. We didn't concede many CCC's though unfortunately we had to concede lots of corners, which often resulted in lots of goals (even 3-4 goals from corner per game, quite frustrating).
recently I was using a flat, counter 4-3-3 with defensive mentality and high closing down (inspired by New Zealand at World Cup 2010), trying to keep the ball away from our goal as much as possible. Had a good 1-1 away draw with Moldova wit that tactic.
In friendlies against weak teams I try to use a tweaked version of the 4-3-2-1 that I succesfully use with the club, but I find it very hard to create chances without decent playmakers/inside forwards.
If you have some players good at long shots then use them as much as you can: you might win more corner kicks, which is probably the best way to score goals for San Marino (CB Juri Biordi is my top scorer with 3 goals in 18 matches...). In the same way you could set your wide players to cross often and aim to far post, increasing the chances of winning a corner.
With that said, 0-8 losses against Holland or England are still on the cards for San Marino...