Wingchun 100, Yak Sau, Lan Sau: Welcome back y'all!!! Good to have some of of the old 'chunners posting here again.
Anyway, first thing to develop an explosive entry
don't do what I've been doing lately: namely working more hours, training less, and eating junk food.
So, looking back to when I was trying to get more explosiveness (rather than growing a larger gut to close the gap) I'd recommend that in addition to those supplemental exercises mentioned before, try training by doing
the very same movement you want to improve. Just go someplace where you have a lot of space, like a long empty sidewalk at a local park and repeat that explosive WT forward lunge demonstrated by Emin, over and over again.
Start doing short range forward bursts five times with a right lead, then five more with the left lead. Then do sets of medium range bursts, and finally sets of long range bursts. Continue like this for a hundred yards, then turn around and do the same all the way back. If you have a partner who can hold pads and retreat in front of you, so that you have a physical target to work on, so much the better. Work angles too.
To vary the mix, add in a lead leg kick to start and follow with punching combos. Remember "every kick a step, every step a kick". And like Yak or somebody said before, lead with the strike, not the step.
...Oh, and especially if you are doing the WT "drag-step", be willing to wear out a lot of shoes.

Good luck!!!