what can i do to discipline my oldest son?

Talking to them at 3 isnt going to help much. You have to do time outs and take toys away and then after the crying, begging and teeth knashing is over explain he was bad and if he does it again you will do the same thing.

Discipline needs to vary based on what the behavior is. Talking is appropriate sometimes, time outs (or think times), do-overs, re-direction still works at this age, choices, gentle physical direction, and so on. A couple of things to keep in mind - when talking to your son, make sure you both maintain eye contact. If you make a request, have him repeat it back so that you know he heard you. Break down complicated requests into pieces and give him choices whenever possible (do you want to put away your toys first or your clothes first?) Find what motivates him - generally, anything that leads to his own independence (aka becoming a big boy) will motivate a child - so give him choices to do things by himself or to have you help him. Praise the good behavior when you catch him at it and practice good behavior you want him to learn but hasn't attained yet. Be patient, it takes a lot of repeating before he'll catch on.

Positive reinforcement...alot of patience too. Keep trying, you'll hopefully find something that works. We were big at taking away things when they midbehaved but as soon as they really were sorry or changed their behavior, they could earn it back the next day. Don't give in right away though or they'll have you trained.