Just because police officers come knocking on your door, it does not necessarily mean you have to let them in. Your first inclination may be to comply with their request to enter, but it may not be in your best interests. Police officers, whether here in New Jersey or elsewhere, don't usually make random stops at people's homes asking to come in and conduct a search.
You should know that the U.S. Supreme Court has your back. The country's highest court ruled that under the Fourth Amendment to the Constitution, you deserve the maximum protection against searches of your home. This means that police must have a search warrant in order to enter your home. The main exception to that rule is if you let them in, which you don't have to do.
What should you do before they enter?
First, if you do open your door, make sure that there is nothing within view of the door that you may not want someone to see. Officers may seize anything left out in plain sight and use it as evidence if it pertains to a crime. If this happens, you could find yourself under arrest. Of course, if you didn't call them and don't require police assistance, you don't have to open the door at all.
When police come knocking at your door, you may want to calmly and politely ask them what they want. They may merely be seeking information about a crime not pertaining to you. If this is the case, you may provide information if you have it. You do not necessarily have to remain in the threshold. You could step out and close the door behind you if you wish to prior to talking to them, or you may talk to them through the security chain on your door.
If they wish to enter and search your home, but without a search warrant, you may politely tell them you won't allow them to come in without a warrant. After they leave, you may want to contact an attorney for advice and assistance in case they return with a search warrant. If they do, you may read it before they enter, but you may not deny them entry at this point.
What should you do after they enter?
After the search, officers may place you under arrest. You may find it in your best interests to invoke your right to remain silent by telling officers that you do not wish to say anything before speaking with an attorney.
While many people believe it "proves" their innocence by consenting to a search and making a statement to police, that could easily backfire. All you are doing is protecting the rights given to you under the Constitution. Don't fall for the officers' attempts to make you feel as though you are guilty because you insist they follow proper procedure and refrain from violating your rights.