When your partner is drawn out of position to the left or right, in most cases you ought to move in the same direction. For instance, if you are on the left side and your partner has run far to the right to return an exceptionally diagonal shot, you can move to your right. In this situation, poaching the next shot even from the middle of your partner’s court is just fine.
As you move out of position to assist your out-of-position partner, keep in mind the portion of the court you are leaving open.
If your opponents have the opportunity, they will try to put the ball where you were. You can combat this in two ways. One is to move to a position between where you can best cover the area your partner has left open, and the area you’d be leaving open.
The other way is to watch your opponents carefully. You can generally see what they are planning to do. As long as you are close to the non-volley line, you can move back suddenly, if an opponent telegraphs that a ball will be placed where you’ve left the court open.
In this latter situation, you might even keep your feet in a wide stance with your knees deeply bent, and jump just a bit a split-second before your opponent returns the ball. As you land, you can then vault to the left or right as needed.
When you watch good pickleball, you’ll notice that partners tend to move so they are standing an equal distance apart in most situations.