Don't try to introduce too many characters all at once. ("Too many" is more than two, maybe three.)
One technique, for example, is to do your opening scene with chars A & B. In the course of that scene, they briefly mention chars C and D. (Again, not more than two or three.) Little or no detail at that point -- a name and one point of connection is enough, such as "brother Joe" or "neighbor Martha".
A scene or two later, you bring C onstage with A, while B goes offstage. Now we learn more about C and also mention char E.
Depending on what you're doing with POV, you might switch over and show a scene with C & D next. They then mention char F. And so on.
Also, don't give a character's entire backstory the first time they come onstage. First, the reader doesn't need to know everything you know. Second, once you have introduced the char with a few highlights, you can reveal additional backstory in little dribbets as you go along.
Oh, another thing, don't use a scene solely for the purpose of introducing a character. The scene needs to advance the story at the same time.