as a ''manager'' of a team projected 16 out of 18 in the 3rd tier of croatian football and had 12 clean sheets in 18 matches let me give you an advice
every tactic works, if you put work into it, not a lot, usually preseason matches are enough,
have 3 tactics, one for weaker teams , one for teams that are stronger, one for teams that are similar,
have a good scout scout your next opposition and listen to what he suggests as prematch training
Look up articles of teams you think are defensively sound and see if you can use their principles on your team.