Increasing your foot turnover (cadence) and adding in intervals to your training sessions is the best way to increase speed.
Trying to consciously increase your stride length in isolation doesn't generally work; and can in fact lead to overstriding, poor form, and hip or knee problems.
The way to run faster, though, is to run faster (obvious as it sounds!) - and let it come naturally. While you're out on a steady run, add in some intervals, even if it's just sprinting to the next lamppost or bench. When your body learns how to run quicker, you can then more naturally speed up in "normal" running, outside of intervals - and with that will come a longer stride length and a faster turnover.
What I would also say is that stride length doesn't vary hugely until you get really quite fast, and are properly sprinting.
My half marathon pace (7min 30 miles) and my full marathon pace (8:15 miles) both look much the same in terms of foot turnover and stride length. It's only in speed sessions of v short intervals that my form looks "right" and I get the longer strides, the triple extension, and my heel kicking back towards my bum that you see in proper runners.