I my field, research indicates that time outs are the most effective way of curbing bad behavior, however, most parents do not know how to use the procedure properly.
You must have a timer, and you must have a time out spot that is free from all distractions or reinforcements (ex, toys, tv, phone, etc.). This could be a stair way (bottom step), bathroom, or a corner of a room where they can not see TV etc.
Some parents use benches or chairs, I have found a rug used specifically for time out works fine and is a cheap alternative to the "time out seats" on the market.
Give the child 1 minute of time out for each year of age, if the child gets up, back talks, cries, etc. give an additional minute up to 10 minutes. They key is to remain calm during this time, no yelling on your end, just simply say you don't want to sit, you get another minute (this is the hardest part for most parents).
If you reach 10 minutes, you take away something that they value, a favorite toy, tv time, phone, etc. it all depends on what your child values and of course their age.
It takes about 2 weeks of doing this consistantly (consistancy is they key)for it to begin working, so don't give up if it isn't working the first few times.
An alternative option is a token economy system where you reward good behavior rather than punish bad behavior. You can use stickers, actual tokens, puzzle pieces etc. When they get a certain number (determined by you) they get rewarded (a predetermined reward that they value, so they know what they are working towards). Again, consistancy is they key and these two interventions work well together.