The University of California (Berkeley) which has one of the strongest college programs in the United States has posted a strength training program for their players online. I've had some success with it after tweaking it to meet my own needs. See
Don't forget to do a little work on your throwing, hooking and scrummaging too, best to maintain your playing skills as well as working on your physique.
Being a hooker you are in the center of scrums and ofte mauls. If you are in scrums you need a lot of leg power and also you need strong shoulders and arms. A great exercise to strengthen your legs is to do squats. The best way to do aquats is with weights ( a bar on your shoulders). You should put the bar on your shoulders, keep your back straight, and then bend your knees and then stand up. Remember, dont over do it on the weights as you will just injure your back. You can also do squats without weights but i dont think it is as effective. Try to do as many as you can but DO NOT overdo it. This will increase your leg power alot! not just in scrums but when you are tackling and for bursting through the tackle. For your arms i advise to do pushups and bicep curls. Makesure to do pushups everynight and not just everynow and again. Hope this helps! :)
Push ups + pulls for an half an hour