The first thing you will need besides your game cartridges is a gamebit and a screwdriver to put the gamebit in, you will also need an eraser and some type of cleaner or disinfectant. The cleaner is not for the contacts, please do not put anything on the contacts, rubbing alcohol, windex or any other easily attainable cleaners will leave a residue and contain water which will cause corrosion, we will just use the cleaner to clean the compartment that houses the contacts so you can remove 25 years worth of spit from people blowing into these games.
Step 1: Gather Your Games and Supplies
After you have everything you need find a place where you can make a bit of a mess, you will get a lot of rubber all over yourself and your work area.
Step 2: Open Your Game
Now just open you game cartridge and be careful not to lose your screws.
Step 3: Cleaning Your Contacts
After you have the cartridge open and the circuit board out of the cartridge, look at the contacts, they will look dirty and might even have corrosion. At this point take your eraser and clean the contacts with it. Go across the contacts and make sure you don't neglect the contacts closer to the sides, most people tend to clean the center very well and not ends so make sure you clean those too.
Step 4: Before and Afters
Let's look at some pictures of before and after and you will see the huge difference this method makes, it's cheaper than using alcohol or any other chemical and it will not damage your contacts, almost anything else listed on other guides and tutorials will end up causing your contacts to corrode. I'm going to say it again, please don't put rubbing alcohol, or ammonia, or vintages, or winded, or any other random crap people tell you to use to clean your game contacts, specially if you have an expensive or rare game as you will most definitely damage your game. Also don't blow on your cartridge, people have been doing it since the 80's and it has been nasty all along, if your game isn't reading properly blowing it won't fix it, just clean them properly and clean your connector inside your console as well, the only reason people think blowing helps is that they pull the game out they blow it then they reinsert it and that is what helps, because it pushes grime and dirt up the cartridge and down the console otherwise it's just disgusting.
Step 5: Now to Remove the Spit...
Now use some rubbing alcohol or any other cleaner, I had a can of contact cleaner on hand that I was using to clean my boards earlier so I used that but the choice is yours, I prefer something alcohol based so it dries faster, but you can use soap and water if you like, just don't put the board back in for a few hours if you use water. I highly recommend you don't skip this step, just think back on the last 25 years and try to calculate how many times some random guy has blown spit and little pieces of Cheetos into your cartridge, it's disgusting and disturbing.
Step 6: Close Your Game and Enjoy
Now all that is left is closing your cartridge and enjoy your game, if you did a good job they won't need to be cleaned again for years. Cartridges were made to last and they probably will outlive us all, with maybe a capacitor fuse and battery change they will still be here in 100 years as long as you don't blow into them or put any water or alcohol or other crazy chemical some clown on YouTube told you to use.
Thanks for reading and I hope you use this technique in the future.