If you're playing DD or ARMA:
Use TAC while attacking a province with a high amount of units on it to help your troops. If it has a small amount and they're not dug in then you may use them to keep their ORG down(interdiction).
If you got CAS use them on moving troops (attacking, fleeing or simply moving does not matter much, tho more effective vs fleeing ones). If you got no CAS use TAC.
INT are good to keep enemy bombes away and for air superiority, although im my experience fighters are superior for air superiority.
Also a word of advice, if you got "old" models of tac don't use them on troops that aren't being attacked, or worse dug-in ones, they may not only fail but also lose lots of str.
STR are good if you want to tear your enemy's IC down, but they are rather useless and a waste of IC if used against big targets such as germany france SOV or the USA. They do miracles vs GB thought. They can also be used to destroy an enemy's infra but tac do that job quite well so no need for str for that sole pourpose.
TRA are good to get some key provinces you can't otherwise get to, using para troops ofc (again awesome vs brittain).
NAV will tear most fleets appart but be carefull not to send them w/o an escort because they are very fragile. If you got no NAV, use TAC since they perform well and only slightly worse than nav in most situations.
Hope that helped you

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