In under a month you will find it pretty hard to mae a big difference. Without sounding harsh, expect to loose some hard earned muscle here aswell. Sucks, but training for any sport takes a huge amount of energy and dedication towards reaching the specific fitness requirements of your position or role.
Plyometrics as you have already mentioned will help. Plyos can fuck you up if you do not do them properly so dont just go down the track or gym and start jumping around. Get someone who knows there shit to show you.
Short and sharp sprints (can use a weighted sled or harness if you like....that works well). Doing explosive/fast lifts is key so:-
Power cleans
Push Press
High Pulls
Power Shrugs
Squat Jumps
Hang Cleans
Clean and Press
Snatches
Also look up the "bear complex" on you tube. That is wicked for power/conditioning for a sport.
There are also methods such as bench pressing (reps 1-4) followed by clap press ups to failure. Squats (same low reps) followed by bodyweight jump squats....emphesis the power element of the clap press ups and jump squats - explode with each rep.
I used to play semi-pro rugby over here, not sure if you guys really know what rugby is but its alot like american football in terms of fitness training/demands. I have done my fair share of this sort of thing. All the best for the season.