IM swimmers have to well rounded in every stroke.
Since fly is your best stroke go out fast, don't shorten or tighten up on your stroke, keep it long and strong and use your start and turn (if in a SC pool) to maximise your efficiency. Whatever you do, don't hold your breath or breathe every 3 or 4 strokes on your fly because this will definitely cause your muscles to fade because of the lack of oxygen. I recommend breathing every 2, but just remember to keep your head still and chin low. Keep a high stroke rate, and when racing against others, set yourself a goal to be in front by backstroke.
From your turn from fly to back really use the under water phase (it is faster and covers a lot of distance without using a significant amount of energy). Since you are on your back you don't have to worry as much about breathing intervals, so that's one problem off of the list. Kick hard, your arms will be more tired than your legs (have you ever heard the expression 'they're going to their legs'? it means that the arms a finished and legs have to do the work) and keep a good stroke turnover, really work on catching the water and finishing your stroke cycle. Since your back stroke is quite weak, it and the breast are the areas you need to work on the most (try harder during the race at and really use the turns).
Breaststroke appears to be your weakest stroke, like fly keep it long and strong, do not elongate the stroke too much, but do not make it so short you're not gaining anything from the glide. Really use your turns on breaststoke as you can get a good 7 metres off the wall at speed. Do not pull up to high or dive to low as this causes drag and will most definitely slow you down.
Freestyle is where you should really use your legs, don't breath too much either as this adds about 0.4 to 0.8 seconds on to your stoke turnover. You need to be mentally strong to finish the last 50m fast, do not worry about your muscles dying cause the race is almost over so give everything you've got.
Keep the fly at around 29 to low 30 pace, back stroke really needs to be about 34 - 35, breast 42 and free 32 - 33. So in short, work the first 100m use breast stroke to get your breath back and max your freestyle. That would give you at time of sub 2.20.
To combat the LA then you must try your hardest in sprint sets and Lactate Production and Lactate Threshold sets to be able to over come the Lactate Acids build up. Also, work on your stamina and go out for a run or go to the gym.
Hope this helps!