Conditioning....sprints say 20-30, 10-20 seconds full speed sprints or what ever you can push yourself too but no jogging...jogging only makes you a good jogger and in rugby you need to do more than jog . And use putting on that weight to your advantage start lifting weights so you can turn fat into muscle and some sort of core work out...you really need a well rounded workout to get in shape for rugby.
personally i prefer circuits and they don't get boring and each set lasts about 30sec-1min heres a quick one of the top of my head wide-base push ups burpees plank `100m sprints sit ups burpees horse tow (you wrap a rope around you and a partner provides resistance) push up - punch bag (do a push up then punch a tackle bag or some sort of bag for 3 then repeat) push ups close base push ups you will need a bit of space for this but after about 2 you become exhausted quickly and then its hell but it works if you think thats a bit to upper body concentrated you can make a better fitness one but it's jsut about stuff that tire you very quickly
