2
People usually cross to bring more power to their punches. You should cross after a few jabs. I told you what the reason for this is already. As soon as you cross, your opponent will think you are about to jab because they blocked so many jabs already. This will confuse them. You can use crosses to hit directly at the face. The opponent will still be able to block it but not as easily because this was sort of a surprise attack.
Hooks
This is another surprise attack. You can use it either after a few jabs, or crosses. You can use this to hit the side of someone's face as explained earlier.
Uppercut
Use this when the opponent is very close to you. This is a very nice way to get the opponent away from you and on the ground. It hurts terribly. The only bad thing is that it is very easy to block. Only use this as a last resort because enough force might really hurt the person very, very badly. You should use this out of nowhere. It is best to do this when the opponent is getting weaker and weaker. Try using this after a few crosses.
Combat: Defense
It is wise to learn to block the same punches you know how to attack.
Jabs
This is an easy one. All you have to do is step back and viola, the punch has been dodged. Everytime someone throws a jab, just step back.
Crosses
This is another funny, but cool one. About ninety percent of the time, people throw crosses right after jabs, so I know this will work very well. After the jabs, wait till someone throws a cross at you. The cross will take longer for them to execute. Instead of moving back this time, I want you to grab the cross and pull the opponent in towards you in a very fast motion. Move out of the way and let them drop to the ground. Never let your guard down though. You never know how fast they will get up and attack you.
Hooks
These are difficult punches to block. The reason is that they are coming from the outside and are hard to focus on. They aren't too difficult though. All you have to do is block with the same hand the opponent is throwing his punch with. Open your hand and just push over to the side of the face she/he is trying to hit. What this means is, he punches with his right hand to hit the left side of his face. You use your right hand, open it up, and bring it to the left side of your face and slap his punch out of the way.
Uppercut
Easy. Just step back.
Practice as much as you can. You can combine chi with these punches to make them faster and stronger. You will surely win the fight.
Defense
Kicking