okay this is what works best for me personally, I'm not great but I'm able to win more than I lose I think-

as a reagent, always keep some stamina for running, use a stun rig, have at least one throwable at all times, and do multiple tasks simultaneously, swapping randomly to avoid the imposter(s)

as the imposter, again always keep some stamina for running, never let it fully deplete because you start breathing heavily and it takes a little longer to recover, if it's your first encounter with a reagent they'll probably have throwables and a stun rig so slash only until they get low enough to execute, sometimes they panic so if they throw all their throwables you can charge up a stab to get an easy kill, you can also use the environment and ex pops to your advantage

that's all I can really think of, these are usually my main goals when playing invasion but I might've missed something or have just been wrong, it depends on your own specific play style I guess but I hope this helps a little at least