Do you what to do and what not to do? Does your business have appropriate response procedures in place? Any have you trained the person most likely to receive the agents (a receptionist, for example) on how to appropriately respond?
Here are some suggestions.
DON'T panic. Yes, this is a very serious matter. But now is the time for a calm and measured respond, not panic.
DO move the agents into a conference room or other private area. You don't want customers, vendors, employees, or anyone else wandering into a common area and asking why the FBI is there. You should get zero pushback from the agents in response to this request.
DO remain professional and courteous. Your employees will only make matters worse if they are rude, disrespectful, or violent towards the federal agents. They aren't the enemy. They are doing their job just like your employees should do theirs.
DO notify the appropriate people. This is not the time to go is alone or hide anything from management and the C-suite. This usually includes the company's highest ranking executive.
DO call your legal counsel and await their arrival. If there was ever a time to get your lawyer involved, this is it. You should also ask the agent to wait for their arrival before starting their search. They don't have to honor that request, but they often will as long as it waiting won't unreasonably delay the search.
DO check credentials, read the warrant, and copy the warrant. You have to right to confirm that the agents are who they say they are, that they have an actual warrant, and what the scope of that warrant is. You also should keep a copy of the warrant for your records so that there is no misunderstanding later.
DO watch and record everything being searched, and seized or copied. This includes where agents go, what they search, with whom they speak and what was said, what was seized or copied, and what damage was done, if any. At no time should an agent be left alone anywhere within the facility.
DO assert privilege and the confidentiality of trade secrets where necessary and appropriate. Just because an item is listed on a warrant doesn't necessarily mean the government is entitled to it. If it's privileged, mark it as such and segregate it; your legal counsel should be able to negotiate how these documents are handled and a judge may later have to determine the government's entitlement to them. If it's a trade secret, mark it as such; the agents should be able to leave with it but its use could be limited because of its status as a trade secret. In either case, you don't want to waive privilege or trade-secret status by doing nothing.
DO engage a communication strategy. If federal agents are executing a search warrant the press probably isn't far behind. You'll want a calculated and uniform strategy in place as to what you're going to say.
AND DON'T under any circumstances make matters worse by refusing entry, destroying documents, erasing computers, or otherwise trying to dispose of "evidence." If the FBI is at your door with a warrant, the odds are high that you're in deep enough hole already. Don't dig it any deeper.