Hi, my name is Brandon. I did triathlons almost a decade ago and now I'm trying to get my mid thirties body back into shape to do them again. The run after the bike has always been really hard, hopefully I'll find some tips on here to help out!
My experience is the best way to overcome dead legs after the bike/run transition is to make brick workouts a regular/frequent part of your training program. Those are not easy, and for a casual BTer, are difficult to fit in. You have to be creative, though.
At one time, I had a public shower at (or near works too) my work...I would bike to work, run, then shower. You'll have to employ commuting techniques to handle clothing and gear. I would also bike to a local track, do an interval workout on the track, then bike back home EARLY in the morning.
Read articles on this site and books on the subject. Joe Friel's "The Triathletes Training Bible" has been an excellent resource for me.