1. Push-hands practice is supposed to be a way to practice and train using the four directions of power (jin) with a partner. If you use local muscle or strength, you never learn to train the four directions of jin. (Or, by definition, you will not be training jin at all.)
2. The jin must be maintained at all times and its potential should be ready to be manifested wherever your partner touches you. You must stay relaxed (i.e., "song" or "sung") to do this.
3. The jin to the hands and arms, and the hands/arms themselves, are manipulated by establishing a ground path to that area and manipulating it with the waist. The control by the arms and shoulders has to be relinquished in order for this to happen.
4. It is difficult to learn to control the arms with the waist controlling the ground path. Single-hands push hands practice is a good way to start. Double-hands patterns are the next step. A great deal of pattern practice should be used to fix this mode of movement before "freestyle" pushing hands practice is done.
5. When someone pushes you or gets you in an untenable position, it is FAR better to step out and lose than to stiffen and resist your partner's "win." If you stiffen, you develop the bad habits of tension and local muscle usage that you should be trying to avoid. Just lose and avoid developing the bad habits that leads you away from jin usage. "Invest in loss."
6. Never let your opponent come in too close to you without some control of his centre and direction. That is what a "ward off" feeler is for. Many, if not most, losses can be attributed to allowing your opponent in too close without control.
7. Always maintain a jin connection. Always keep that jin connection so that it goes under the jin of your opponent. But never offer resistance.
8. Your contact with your opponent should be light. Lightness without jin is useless and is not Taiji.
9. Focus on the balance of your opponent; don't get involved in "arm-and-hand" games and don't let your hands and arms get led too far away from your centre line. Think globally, not locally.
10. "Cheat" by always working on your leg strength. The stronger your legs are, the more you can let your source of power come from lower down. The lower and stronger your source of strength, the more advantage you have in push hands.
11. Constantly monitor yourself for how "pure" (i.e., free of local muscle tension) your jin is and how relaxed you are. Find the areas where you were forced into using strength and correct those for the future.
12. Learn to send any incoming force to your feet. After a while you will automatically start bouncing people away. Get some training on how to increase your jin abilities.
The following YouTube video shows Chen style push hands with Chen Zhenglei and Wang Hai Jun
Ma Jiangbao (Wu style tai-chi) demonstrates his push hands skills at a seminar in this video