Step in and strike at the first sign of movement of your combatant. Do not wait for their strike. Do no over-extend your body. Especially if they are bigger than you, ensure you are close enough to be in your optimal range. Maintain structure. Strike and continue to control, keep them off balance and cramped as you follow up. Your attack is your best defense and gives you the advantage.
When rolling, imagine your arms are around a witches hat - wide bit at your body, small end is your hands. Imagine your arm and hands are drilling into your partner's chest. Also, when you come down from bong sau to pierce, this should be going forwards too. It is a strike and your partner will need to be defending against it with the arm doing the fook sau.
The "party" counter arm grab using elbow over (left hand grabbed by right, or right hand grabbed by left) ends with drawing the opponent's hand towards your body. Imagine bringing your elbow to your ribs (this avoids bending or leaving stance).
The "party" counter arm grab using wrist and fingers pointing down (left hand grabbed by left or right hand grabbed by right) starts by moving around the force the opponent is placing on you (circular move, often around and up) and ends pointing your wrist and fingers towards the ground (where you want your opponent to be forced to go).