Jathran and others who have problems getting screen protectors to apply perfect without bubbles.
You know what the trick is and it works 100% of the time? It's water. Take the screen protector and wet it completely on the side that is going to go on the screen. It doesn't matter if you get it on the other side so don't worry if you do. You don't need to dry it if it does get wet. So.....Once the screen protector is all wet shake it one time. Then go to your device (DS or whatever it does not matter) and put the screen protector down being careful to keep it centered. Now just use a credit card or something completely similar and cut in about half long ways which is horizontal (cutting the credit card in about half is what you do with the DS/DSi/3DS but if your applying a screen protector on an iPhone you wouldn't need to cut the credit card as there are no borders around the screen to get in the way of the credit cards movement.) OK, now the screen protector is centered on your device (DS) and you'll see a little bit of water under it, which is wonderful
At this point make sure to have something like a microfiber cloth to dry up the water you are going to remove from under the screen protector. Microfiber is great
My suggestion is to buy one if you don't have one and their cheap. To get the water out from under the screen protector and to essentially apply the screen protector perfectly (that means no bubbles!) just start at the middle of the screen (for each direction that means top/bottom/right/left) and drag the credit card's edge soomthly to the screens edge (use the credit card's smooth edge, not the edge that you cut!) It's so simple
Dry the water you remove after you move the credit card to the screens edge in each direction. Don't worry your instinct will kick in with this step as well as some of the others. Now take a look at your handiwork as your screen protector has been applied perfectly. I've done it this way multiple times and it comes out perfect EVERY time. This will save your 3DS screens or other device screens from scratches. Also, it might be a good idea to use some thin foam double sided tape on the screen bumpers that are located on both sides of the 3DS top screen (on the edges, it's black). Just pry it up as it's glued. Cut a piece of the double sided foam tape to the exact shape of the bumper and then stick it where you just pulled the bumper from or apply it to the bottom of the bumper if you want and apply the bumper back from where you got it. It works well and it's quite fast as well as easy to do.