I find that when the stranding is changing colours 1-2 stitches then the float will even itself out as long as I knit loose.
For more than than 3 stitches, knit your Colour A stitches.
With Colour B in your left hand, give the Colour A stitches that you just knitted onto your right needle a little tug to stretch them out and this will naturally pull out how much Colour B yarn you need to float behind the Colour A stitches.
Proceed to knit Colour B stitches.
It shouldn't pucker, the back loops will be a tad loose but this allows for the fabric to stretch. If it's wool you're using, it will eventually felt. The only big problem is snagging them on earrings, barrettes, nose/eyebrow/lip piercing when you put it on.
Good luck and have fun!