Oh...I played wide reciever and strong safety for a year before deciding that football wasn't really my sport and i switched to boxing, but here is what i did to keep my starting position:
Speed: I would strap nylon weights around my akle/shin area and then run sprints...you dont have to do it this way, really any type of sprints with something strapped to you/tied to you/forces any resistance in any way that is moderately heavy(dont want something too heavy, that would hurt

) forces you to make longer and faster strides, but be sure to keep running in perfect form or else you wont really get any benefit out of it...
Power: Like i said earlier...squats. Obviously excercise all of your muscles so you dont have any imbalances, but squats are extremely important to build explosive power which is needed for every position, so try to master your squat form. Also, with the lower body power that squats build it will make you a much better blocker...and coaches
LOVE recievers that can block well...it really sets you apart from everyone else and catches their attention.
Hands: well speed and power are great, but they're useless for a reciever if you can't catch and hold onto the ball! Try fingertip pushups to strengthen your hands(just like normal pushups, but you go up on your fingertips instead of palms) and incorporate wrist curls into your routine, they're great for builing up your forearms and grip to hold onto the ball once you do catch it.
LAST NOTE: All of this stuff may seem like alot, but the most important thing about training for football is... REST! If you don't rest enough, all your workouts will do is destroy your body, not build it up. I'm sure you already knew that but i just wanted to remind you

...I know sometimes while training for sports, especially when the start of the season is close, you get impatient and sometimes overtrain because of it...but in the long run this won't help you at all.
OK, hope you didn't get a headache reading all of that!
Peace out!
