Run! This is one of the best things you can do - no matter what your place on the field. The thing that distinguishes Rugby from football is everyone goes non-stop, almost like soccer (but worse because everyone except the full back is moving with the ball all the time). Even if you're a prop or a second row you'll still need to be running so you can make tackles. Running is probably the single best way to improve your game.
Do up/downs. What are up downs you say? They're like squat thrusts. They are useful because you are constantly getting hit in Rugby, or hitting someone else, and you need to get up quickly. You'll also need to dive on the ball, tackle, and generally haul @#*. Make sure you're pushing yourself beyond the point where you think you can't do anymore; by the end of a game you are so tired you can't move your little finger, but you have to keep going. Up/downs show you how conditioned you really are.There are 2 ways to approach up/downs:
As a team: Everyone lines up on the field (I prefer to do them in an exploded scrum formation) and the coach blows the whistle. On the sound the team gets onto the ground as fast as they can - face down. On the next blast everyone gets up as fast as they can. Repeat. This should start out slow, giving time to get up and down, and increase in intensity until it is constant.
Do it solo/in a small group: just get you your butt up and down as fast as you can and as long as you can.
Start lifting weights. Go to the gym and get someone on your team to show you a lifting routine and then make yourself do it. Pack players should be looking to increase muscle mass, while backs should be looking to increase tone. Tailor your routine accordingly.
Now I don’t agree with the guys or gals who want to eat 40 percent protein in their diets. It’s way beyond what is scientifically proven to be required, expensive, not necessary and may even be unsafe in the long term.
However, heavy weight trainers can probably justify extra protein up to about 1 gram/pound bodyweight. Don’t make it all beef dripping with fat though. Get plenty of white meat, dairy protein and soy as well for healthy eating. Get some advice if you even think you have dysfunctional kidneys. Just for the record, 4 ounces or 100 grams of lean grilled chicken breast or beef has about 30 grams of protein.
Creatine and zinc are potentially important components of an anabolic diet. Creatine builds bulk and re-supplies the phosphocreatine energy system which is important for those fast heavy lifts and zinc is necessary for testosterone production. Meat protein is a good source of both of these elements. Vegetarian bodybuilders may need to ensure sufficient intake.
Workout Strategy. Heavy lifting and high-intensity workouts raise testosterone, growth hormone and IGF-1 but cortisol goes along with them during intense exercise. This applies to sprints and other high-intensity programs as well as weights. Planning your nutrition is likely to be helpful.
Good luck in rugby season and your training days! Eat healthy! Plenty of protein!