There are certain score situations, like 15-30, 30-40, Ad-out, etc. when you must choose your shots carefully.
Avoid going for low percentage shots (drop-shots, hitting too close to the lines, too much power, etc.). Instead, use the strokes that you feel comfortable with.
If the groundstroke cross-court works for you very well, then use it in the pressure points. If you have a good slice serve, use that on both first and second delivery - anything to keep the ball in.
If you have to play your weak side, direct the ball towards your opponent’s weak side as well; or cross-court for a bigger margin for an error (more court, lower net).
Be patient on the pressure points and do not try hitting winners to end it quickly.
Use breathing techniques (inhale as you prepare, exhale as you swing) to calm your mind and body.