Most intermediate players plateau at the same place. The forehand is solid, the bandeja is workable, the smash lands in. And yet matches against stronger pairs keep ending the same way. The gap is almost never technical.
First habit: stay connected to your partner. Advanced pairs move as a unit, with no more than four to five metres between them at any moment. If your partner pulls wide to defend, you slide with them. If they attack, you step up. This single change wins more points than a new racket ever will.
Second habit: talk on every ball. Call yours, call out, call the lob early. Silence is what causes the two of you to leave easy balls in the middle and chase impossible ones in the corners. Good communication is louder and more boring than you think.
Third habit: pick the right ball to attack. Intermediate players smash everything that floats. Advanced players let the high, deep ones bounce and put the short, weak ones away. Patience is a weapon.