What alerts you to a squib is what is called a "pop and no kick". The hammer drops, the gun seemingly does not fire--or may fire weakly. If this is the case, and it happens to you, don't get too upset--just clear it as follows.
First and foremost, SAFETY---KEEP THE WEAPON POINTED DOWNRANGE AND AT THE TARGET FOR AT LEAST ONE FULL MINUTE. This gives hangfires a chance to go off. One time, I believe that some bullet lube found its way between charge and primer, in my .44 Mag. Dropped the hammer, no shot. Kept the handgun pointed downrange, and heard a sizzling sound, coming from the gun (!). After about 10 seconds, the round discharged with full power and velocity!!
Next, after a full minute has passed, CLEAR THE WEAPON. No shortcuts. Remove the magazine in semis, carefully open the cylinder in revolvers.
In semi autos, CAREFULLY draw back the slide, and observe the ejection port. Eject the round onto a soft surface. Did a complete round eject? Check the primer for an indent. Just the case? (maybe with some powder granules?) BE CAREFUL. YOU MIGHT HAVE A BULLET STUCK.
In revolvers, carefully open the cylinder. If it doesn't open, check the barrel/cylinder gap--the bullet might be stuck there. If so, take a dowel and push the bullet back into the case. No bullet?
IT MIGHT BE IN YOUR BORE.
DO NOT FIRE THE GUN AGAIN, OR EVEN LOAD IT, UNTIL YOU CAN TAKE A CLEANING ROD, WITH PATCH, AND PUSH IT ALL THE WAY THROUGH THE BORE. Don't even trust your eyes with this one. Putting a patch through will tell you if there are any obstructions in the bore. Use a tight fitting patch, too.
Final note: Most squibs in revolvers can be blamed on using slow-burning powders in small quantities. H110 and W296 are notorious for this. Follow the manufacturer's recommendations explicitly. In semi autos, usually the problem is low powder level, or even no powder.
It is'nt hard to clear a squib; just keep your head on, and you'll be OK.