First and foremost, you can't teach rhythm, it comes to you. Some people like to get a metronome, but I would advise against it.
When you play a song, play it how you feel like playing it. You don't have to stick to strumming patterns just because XXXXX does.
If your in trouble, the best piece of advise i can give you, is SLOW IT DOWN. Strum down, whilst saying ONE out loud. Then when you come up say AND out loud. At your own pace. Don't rush things, practice.
As Livebaitman said, First things first, don't rush yourself. Learn your chords, practice them, build up your rhythms in your head, then when it all "clicks" it will be a lot easier.
A very simple pattern to learn is ticket to ride.
1 & 2 & 3 & 4 &
------0------------------0
----------2--------0------
-2------------2-----------
---------------------------
--------------------------
--------------------------
Rinse repeat, if you pick it close to the rhythm it should sound spot on.