The absolute easiest way to become a more successful doubles players is by finishing off points where you've gained an advantage.  In most cases, that means winning the point when you get a high volley.  The reason it's the easiest way is because you don't have to hit a higher quality shot:  More power isn't needed;  Perfect placement isn't needed.  All you have to do is hit it to the right person.  And that person is the opposing net player who doesn't have time to react to defend.  Just aim right at their feet.  If I hit a medium-paced shot "to", "near" or "at" the opposing net player, they only have about 0.3 seconds to react.  If I hit it back to the player at the baseline instead, they have about a full second to react.  The net player may also be running away or hiding just hoping not to get hit, so it rarely comes back.

In the video below, every point has someone with a chance to attack with a high volley.  The player with the high volley:

Won 33/39 points (85%) when they hit to the right place (toward the net player).  And you'll notice that in every case, it's very obvious because the ends there.

Won 8/18 (44%) when they hit it back to the player at the baseline, and it's hard to notice because the point just keeps going and then one team happens to win a few shots later.

The 44% above seems is about half, but this was actually a good day for them.  Usually they lose 2 points out of 3 because they or their partner are out of position.

Learning this concept is critical.  There are 57 points here from about 3 sets worth of tennis, all with a put away opportunity.

If they did it right every time, they would win 48 points and lose 9.

If they did it wrong every time, they would win 25 points and lose 32.

An entire set can be won with only 24 points.  If you are not doing this right, you are probably losing 3-6, 2-6 when you should be winning 6-3, 6-2.

The difference is MASSIVE.

Doing this right also leads to other free points.  As players get more afraid of you at the net, they start to miss more and their partner tends to stand farther from the net.  That makes it harder for them to do it right, and you start winning faster and faster.  This is the #1 key to winning high school doubles matches.

It also helps a lot to move closer to the net to make the put away even easier, but that's a topic for another day.