A warrant require some kind of evidence to back it up. Like pictures of know drug dealers and junkies going in and out of a property. You can't go to a judge and say my informant says there is going to be a crime at such and such place and get a warrant unless you have prior acts etc to back it up.
Generally speaking, this type of evidence must also have currency. The photographs of these people doing illegal things would have to be recent.
The process for obtaining a search warrant involves typing up an affidavit, which explains in detail why you think there's probable cause to enter the property in which the crime is supposedly being committed. The affidavit usually includes a list of evidence of the crime being committed, which might include statements provided by a confidential informant, and all the steps taken to find evidence of the crime, such as searching through trash and finding receipts, doing an undercover buy, what have you. The affidavit will also usually contain the personal qualifications of the person submitting the affidavit that show why the person has the ability to make distinctions about why something might be evidence of a crime.
Whether you get granted a search warrant from the affidavit really depends on how solid your evidence is, and what state you're in. Some states are a bit more lenient with PC than others.
This is from a federal perspective, mind you.