I started to also get a sore throat when i started gigging. I found that warming up and warming down worked well for me. The exercises that i did where as follows:
the lip trill and the tongue trill. i would do the lip trill the most working this one through my most comfortable area of my voice on a 5 tone descending scale with a descending slide at the end of it. i would do this for a couple of minutes antil i felt like my vocal folds felt soothed and relaxed, and then i would try to sustain the tongue trill an a comfortable note in my chest voice, as i found this to be great for relaxing the tongue.
try them and let me know how you go, would be great to know.
All the best and i hope that it works for you.