Pushing Hands practice in Taijiquan has impressed me a lot when I had first come across it. Before that time I have learnt Judo and set out to master the art of "yielding" in real fight situations.
This meant pulling my opponent by the arm as it straightened during his punch- or pushing at the moment he is pulling/ retreating.
With karate I have learnt how body mechanics could be used to exert effort against resistance in the most efficient manner. Now- I did not feel the need to "yield" in order to be able to throw my opponent.
Two exercises I have devised build strength, develops proper stance and also helps to develop a good feel for the body mechanics involved in grappling.
In the one exercise- the pulling drill- one partner is in front stance with his reverse punch- wrist grabbed with his partner's reverse punch-hand. Grabbing hold with the captured arm's hand the partner whose arm was straightened to begin with shifts back into back stance and pulls his partner into the front stance position in which he had previously been. (Umm... it is not necessary for me to say that "he" can also be "she", right?)
After that roles get switched as many times as you have time for.
Another exercise starts with one partner in a front stance with his forearm out the the classic peng position of Taijiquan while the other is the guitar-playing posture pushing against that forearm. Driving with the legs the pushing partner will end up in forward stance while the other ends up in cat stance (or that toes-up stance in the guitar-playing posture). From here the partner with his weight on the back foot now pushes against the forearm of the other. And roles switch for as long as time allows.
In Wenhsiuquan classes these drills are used as warm-up exercises- so we do not spend a lot of time on them. Resistance can be increased and decreased as the need arises. The exercise will not work if either party's balance becomes off-balance. Best way to prevent it is to not yield too much, but also not to be too immovable.
You may try this at home with a class mate from your dojo or, if you are an instructor, make it part of your class warm up.
Have fun and train well!