1 lap sprint: practice your starts from being held. In a race that short, the start matters a lot, and if you're gassed from chasing back up you can't sprint. Pick someone faster than you in the sprint who's likely to win and sit tight on their wheel-- follow them as close as you can through the sprint and try to get around at the end. If you can, you might win, if you can't, you'll still get a good place.
Pursuit: is it what we call "australian pursuit" where people are uniformly spaced around the track at the start, you get pulled when you're passed, and the last person on the track wins? Or more like a 3 lap time trial? If it's the latter, work on maintaining a steady high speed. If it's the former, your start will matter a lot-- you don't want to get caught early because of a bad start-- you want to have a good start and pick people off slowly (maintaining the highest speed you can maintain steadily)
3 lap scratch: As an endurance rider, I'd sit on the back, attack hard and wide (inside if the pack is outside, outside if the pack is inside) and make them chase. If you surprise them you'll be at speed before they can react. If they're gaining, ride at ~85% and let them catch, go to the back and do it again (and don't let them recover). Each time the "pure sprinters" will stare at each other hoping someone else leads the chase, letting you get a gap and making it harder once they do chase. If they're likely to catch you, you don't want to be going 100%, you want to be going at a steady tempo you can recover from so you can do it again shortly after getting caught. In a 1200 m race you might get to attack 3 times. If you're making the gap bigger while riding tempo, slowly ramp it up, and then go full out with 3/4 to 1/2 lap to go (depending on how far you can go at absolute max)