You want your will to be as complete as possible so that there is no confusion after you pass away. However, that doesn't mean you can put absolutely everything in it, and it's important for people in New York to know what they should leave out.
For example, it's something of a waste of time to put funeral plans into a will. You can, but your body itself is not legally allowed to be part of your estate. This means that no one has to honor what you write in your will regarding burial, cremation and all the rest. If you have specific desires, just talk to a family members that you love and trust and tell them what you'd like them to do.
You also don't want to put anything you own jointly into your will, unless you're simply noting that it should pass to the other person who has an interest. That's what's legally going to happen, anyway. For instance, if you and a partner own a store together, with the deed in both of your names and a 50/50 interest, then it's going to go to your partner if you pass away. You can't leave it to a third party.
Finally, you don't want to put in anything illegal, like illegal drugs, illegally owned firearms, stolen property, and the like. You also can't make any requests that are illegal, instructing people to take illegal action on your behalf—for instance, asking them to bury you on land you don't own.
When writing a will, be sure you know what things to include and what ones to skip.
Source: FIndLaw, "5 Things You Shouldn't Include in Your Will," Brett Snider, accessed Nov. 25, 2015