If you know the rules of tennis, you are in a good place already. Padel is always played as doubles. Basic doubles tactics work well in Padel. But once you get better, more tactics come into play.

You have two underarm serves. 
To serve, you bounce the ball first behind your service line and hit no higher than the waist. 
The ball has to bounce in the opposite service box to count as a good serve; BUT, if it bounces and hits the mesh side fence, it's OUT! 
If it bounces and hits the side glass, it's GOOD and should be played if possible. 
The ball has to bounce on the opposite side before it hits a wall (unless it is volleyed) If the ball hits a wall directly without a bounce the ball is out (same as hitting the ball past the baseline or past the tram lines in tennis)One thing that tennis players will find difficult is that once a ball goes past you, you can still recover to hit it after it hits a wall. .. . so patience is key. You can sometimes wait rather than try and get the ball early. 
The Scoring is the same as tennis. 
You are better off being patient and in control of the shots you play. Padel is about control, not power.