Any big hills neer you? If there is get running up and down them
Another great way to build stamina do you know any 1 that does boxing? See if you can get ur self down to boxing once a week join in with there training lots of running skipping ect. Skipping is also good for speed as well over short distances those first few steps where you realy need it.
As for your warm up it should take at least 25 mins warm up i used to do
(NB the was on a 7-a-side pitch)
2 Slow laps of the park to get blood flowing loosen up
Very gentle stretch working all muscle groups in the legs
2 more slow laps but picking pace up along by lines then slowing down again.
Stretch again
2 more laps but side stepping along by lines
more stretching
Suicides by line to 18 yard box, by line to half way line, by line to far away 18 yard box, by line to by line
Hard stretch
same again but change it slightly side steps, jumps, twists.
more stretching
Now as with every thing when it comes to fitness we all have different ways of doing things just what we done before training.
( Oooo look at me giving advise like I am even slighty fit at the moment
)