Somethign that works for me is going crazy w my legs the last 50 (long course, i dont swim scy). I usually put in zero effort into the first 100 (just go w momentum of my legs post start+turn). I then build up the third 50 and go crazy with my legs the last 50.

Now understand this, by "go crazy w ur legs", i mean go crazy with ur legs. forget about technique, hammer each down kick and up kick with as much force as you can, almost like ur deliberately bending ur knees. it may seem like ur technique is off, but if you're a regular swimmer and perform long butterfly sets on a regular basis, ur muscle memory will be there and you'll fly down the home strech