3.5 v6 nissan altima not starting?

-I have had this problem once a month for the past couple months,my car wont start but the battery is new and the starter is working.I took it to the same shop because they can always take my car and have it back same day or next morning.The shop has been putting dry gas in and it has been fixing the problem,but it keeps on happening,it happens about once a month.My car has 130,000 miles,the shop i take it to does good work and are certified mechanics, if i can get it in the shop im gonna ask to get the fuel filter and maybe spark plugs checked,does anybody know what this problem could be or anything else i should have looked at?