Choosing the Right Doubles Partner
To pick the right doubles partner for your games, first you must consider your own tennis game's, (more specifically, your doubles game) strengths and weaknesses.
How to choose a doubles partner in tennis
Once you have made an assessment of your skills level and game, you ideally want to go for a partner that complements your playing style.
For example if you have a Strong serve, you can really benefit from a good net player taking advantage of the opponents weak returns, or if you are a base-liner hitting flat rockets at the opponents you can go for a safer, more consistent partner that uses a lot of spin to keep the ball in the court, as this constant change in rhythm, ball depths, speeds and spins will make it very difficult for the opponents to adapt to your game and beat you.
For the most part, a powerful, explosive player should team up with a safer, more consistent player, in order to have a balanced doubles game since teaming up two explosive players puts them at risk of racking up unforced errors, while two consistent, slower players may lack the explosiveness and aggressiveness to push the opponents for mistakes.
Choosing sides with your doubles partner
When it comes to choosing who will play on which side, generally, you want the "overall better" or "safer" player to play on the ad side (the left side), since this is the side with the most important points being played on (such as ad-40, 15-30 etc.).
You can also choose to play on each side you wish to hit more shots from, for example a right hander that prefers forehand will play on the right side and if the same person prefers a backhand will play on the left side.
Also if there are one left and one right hander on the same team, it would make sense to play on the left and right side respectively since you will both have your forehands when playing cross-court.