If so, what kind of stretches do you do? And is there any way to delay a build up of lactic acid in your muscles?
None, static stretching before exercise is not advised (I assume you are referring to static stretches), current best practice (according to current coaching qualifications) is to warm up thoroughly with low intensity exercise, possibly followed by dynamic stretches which generally mimic the exercise to be undertaken, but with exaggerated actions.
Static stretches are advised following exercise, but only short (10-15 seconds) shallow stretches (fatigued muscle is much more prone to injury and should not be pushed with stretches following exercise). Deeper stretches for improving your range of motion etc should be undertaken on rest days, these are generally the same stretches but taken deeper and held longer.
It should be noted that over time, opinions keep changing, but this is the current taught best practice and it makes sense.
Personally, I just get on my bike and go, building up my intensity over the 1st 10-15 mins. Similarly for cooling down, just reduce intensity over a similar period.
As for lactic acid build up, you can either ride slower or you can work in increasing your oxygen efficiency and pushing up your lactate threshold. You might want to read up on Lactate threshold and the widely published interval training techniques that can be used to increase your lactate threshold.