here is something i wrote about lookahead.
lookahead can be broken down into 3 main techniques
tracking - this is the most common form of lookahead where you simply look around while your executing your current pair or even cross. your not looking at what your solving but your looking for other pairs.
remembering - while your looking around your going to see pieces that your not currently looking for. you need to remember the location of these pieces so that when you do need them, you know exactly where they are.
predicting - this is being able to predict the next pair before you even start solving your current pair. this is why the pros can average so fast. but you don't need to be as good as them yet. you just need to be able to predict basic cases such as predicting the next pair when your current pair is just a 3 move insert.
to practice tracking you want to turn as slow as you need until you can comfortably do f2l.
then you want to slightly increase that speed out of your comfort zone. once this new speed feels comfortable you just repeat the process until your back as normal speed. this is easier said than done though. remind yourself every solve to look AWAY from what your currently solving and look AROUND for other pairs.
practicing remembering is easier. it will come pretty much naturally. you just need to think a little bit harder during solves to actually keep note of pieces that you see. remind yourself before every solve to try to remember where pieces are.
to practice predicting. you can simply recognise your first pair, then predict your next pair and then blindfold yourself and solve both of them without looking. you of course want to increase the speed you can recognise 2 pairs at once at so you will need to keep practicing this.