No 1 I am a retired pro mechanic ,with to many years of making small things out of a block of Steel ,Brass ,Aluminum and all kinds of other stuff . The Big Number One , Is buy the best files you can then take care of them .The will last a long time and do a real good job, Cheap discount store files will not hold sharp teeth , Never ,never buy a file that is just advertised as imported .I have seen files from Asia and India ,maybe they save the good ones for the Home market and export the ones that are not made right , You can however buy lots of small files made in Europe , Grobet Swiss are first class . And the best maker of Hand files in the U.S. is Nicholson . Dollar for Dollar they are a best buy . EZE Lap  and Newman make Diamond coated files (not cheap) and cut in all directions ,and they will cut into almost anything ,but are for small jobs and vary fine cuts . Back to Nicholson files ,Their line of American pattern files are ISO 9001 certifed , First of all a file that is for making something that is not real flat become flat ,the file must have a real flat cutting surface ,that is a standard , down to .0001 or less over the lenth of the file pluss or minus 0 ,that flat . A good file that is Square is not a trapazoid even by .001 and a good file that is round is not a ellitcal by even .001 . Thats why you do not buy cheap discount files . And also ISO files must meat a standard of uniform hardness ,so if you are sold a file to be used for cutting cast iron or soft steel ,each part of that file will cut the same and do the job it was intended for .Another strike out for Discount store files . By the way good files are almost always just a buck or two more then junk so why buy junk . Something to think about is what kind of work you are doing so what file is best . Say you are a welder You could buy a set of  3 Nicholson files for hard welded metals for $40  on the other hand if you are doing auto work or home maintenence work yuo can get a set of 4 General purpose files for $21 (see good files are not that bad in price ) but if you are a Machinist you are in need of some real hard and true filed ,that can stand pushing or draging over steel with power of say a lathe . And General Purpose will not work . You will need a American pattern set . 8 files about $72 bucks ,and if you work on something real hard you will need SWISS Pattern files (not made in Asia eather ) A quality Swiss file say 8 inches long 21/32 wide cost $16 each . and a Diamond file about the same size will cost $60 each ,and that file will cut almost anything, glass,carbon,stellite,and hard facing . You might think a file that works on steel should be fine on something soft like plactic or aluminum . You would be wrong ! Plastics will dull standard files for steel and real fast . You can get high carbon steel files for plactic , and Aluminum will clog or load up a standard file for steel . You can get standard files made just for Aluminum and soft alloys ,they have specal tooth design and will not load up . I sometimes use them on copper and brass also , And you just can't believe what a nice finish and how fast they cut . now for wood Steel working files only work on super hard woods and they will not cut much off , For wood get Rasps for fast cuts and Pattern makers or Cabinet Rasp for fine work , When working in water you can get black oxide Maxi-sharp (brand name) files .They resist rusting . Rusted files are scrap files . The first thing that will rust is the fine cutting edge ,then the rest of the file . A rusted file will not cut flat and true and maybe not cut much at all . and if rusted deep the file will brake if layed into the work to hard . always store files coated with a little oil , then clean oil off file before use ,unless it is a lathe file that can be used in water based oils . Always use a file dry and oil free . when you are done clean the teeth out with a file brush and a file pick .Then coat with a light oil or silicone spray , I never liked WD40 on anything after I coated a new 22 rifle with it and a day later it had some rust spots was I ever pissed off , Bolt braker sprays like WD40 are not good for rust proofing , Dry lubes and silicone sprays on files could be the best option and before you use a file Carb cleaner and Brake cleaner would clean off all oils nicely .And if you need to do some real close work ,You can glue a strip of glass to a wood sanding block ,coat the glass with grinding compound and start working in all directions . I have cut a cylindre head flat and true using a thick peace of mirror glass . A finer job than a surfice grinder that cost $20,000 big ones . The cylindre head was 2' by 9" and weight was 80 lbs and came out flat to .0001 +or- .000015 and the best a grinder could do was .0001 + or - .00025 and that was on a good day .Some files that will be OK in a pinch would be Craftmans, (but not Sears non Craftman) I got a file at True value ,not cheap eather (USA) ,it was ok but overpriced , As well as Snap ON (or snap off) ,Ok but way over priced. Mack tools ,Overpriced . Grip on tools (never mind JUNK) ,Also I got a vary nice set of hobby files Made in Englind . The Brits know how to make nice hard steel tools , You would think some Samurai in Japan could do the same .to bad it just did not happen .German steel tools are just fine but we cant afford the prices . Spain (not Mexico) can make good cutting tools for fair prices . Sweeden has great wood working cutting tools and for real fine work you can't beat the Swiss . China ,India ,USSR ,Mexico,.Tiawan .Korea ,(most ot their steel is melted down old US cars )and Japan for files and Drills as well as other steel cutting tools save up just one dollar more and get something that will work From Steel producing counterys like USA,Germaney,England,Spain,Switzerland.And its to bad  China was the first to make things out of iron and it was almost hammered into high quality steel and the Samurai armors of Japan beat that iron into real fine steel ,But it some how was lost .To Bad, .If you liked this info please vote so I know it was helpfull Thanks . Last tip always use a file handle that file hilt can tare you up and blood can get all over what you are working on . If you use a file with a lathe do not have on loose clothing ,a file handle is a must , A last option cut off File Hilt all the way to the hard part of the file and round out sharp edges .The file hilt is made to drive into a wood handle ,Cheap scate out with no handle and you might get some cuts or holes with some blood squriting out good Luck ,and oil coat your files for storage .or store in a very dry place wrap in a oiled rag or air tight box .Rusted Files are scrap for the trash can.