I would tend to keep my distance from Game and Watch as he lacks projectiles. What Sikarios said, just use your range and make him impatient, then wait for him to blunder. Game and Watch's aerials aren't half bad, so I would try to fight him on the ground if he gets close. Remember, Olimar's grab is one of the best in the game, so make use of it (It has little lag anyway, so why not have a crack?)
Once you have successfully grabbed Game and Watch, I'd follow up with D-Throw and then U-Smash or
U-air. If he is near to the edge of the stage B-Throw all the way: Nasty knockback with Blue
If he is in the centre of stage try U-Throw-Nasty knockback with Purple.
I wouldn't tend to combo a lot, so my moves would consist mainly of smashes (My fav would be U-Smash, Olimar's strongest). U-Smash is best for finishing off the opponent. F-Smash has good range, D-Smash is best when the opponent is too close for F-Smash but too far for U-Smash.