if it's on a really small map like luxembourg, you'd rather only hit 1s that are not your target. you need to leave any player that is not your target as health as possible. don't even hit your assassin.
on larger maps, try not to kill isolated troops that are not your target and that will be a pain in the ass for it's assassin to go for.
you just need to keep in mind that blindly going after your target is stupid, you are probably giving the game to someone else, patience and timing is the key. you will make averybody lose and everybody pissed at you. It's very frustrating when someone totally noobs an assassin game and makes everybody lose. If you want to try for assassin, I'd suggest you to do it on larger maps not to piss people off. there is a community of assassin speed games players out there always playing on doodle earth and luxembourg, try to win a little experience before joining those and ruin games and get foed by all of them!