D., I have a 5 year old who is really good at the buttons and pushing the limits. Consistancy is a key. If your child plays with something of yours and you don't want her to, ensure you discipline them every time you see her playing with the item. Letting the discipline go 1 time can have consequences for you! :)
You may have to try many different methods to find out which one works, not all methods work for each child. We started out with timeouts, 1 minute for each year of age. That worked great for a while and then stopped working.
We then moved onto taking away privlages and that is the current method of discipline in our house. Depending on the situtation, we take away either her nighttime books or her tv.
We also have a reward system for good behaviour. We got a "chore" board from target (magnetic) and it has different things, like make your bed, brush your teeth, etc. for the days of the week and each day, my daughter gets to put a magnet up for whatever she gets one for. At the end of the week, if she did a good job, we reward her by letting her do something she wants that we would normally not let her do like sleep in the den.
If you choose to use timeouts, ensure that you do not communicate with the child while they are in timeout. If they leave the timeout space, lead or carry them back to the corner, timeout spot and restart the timer. When timeout is done, get an apology and ensure you reinforce that you love your baby but you don't like the behaviour your baby did.
Also, don't be afraid to put yourself in mommy timeout. If you get really mad and feel you are about to loose it, tell your child that "mommy needs to go into time out to calm down and then I will be able to talk to you when I have calmed down." Ensure your daughter is in a safe place where you can leave her for a few minutes and walk away. This helps the child learn how to deal with anger in a constructive manner.