This is a t-shirt I made for my boyfriend's birthday using bleach.
It's not hard and there are multiple tutorials on here for how to do it, but below are a couple of extra hints I wasn't told before I began!
Use a site like DA Fonts to get a really interesting, subject appropriate text. I just searched 'game' and this awesome retro pixelated text jumped out.
A lot of the texts also have picture texts (like wingdings but better) which are great for simple images.
Make sure you check what it looks like before inadvertently ruining a t-shirt! I cut my image out of a more complex picture, and found that if I looked at it from the back I got a better idea of how much it resembled a computer, keyboard and mouse (I actually ended up flipping mine entirely!). To be doubly sure you can always colour it onto paper using a pencil as a test.
Try to use a simple, blocky image without too many fiddly bits. The more complicated bits, the more chance of it coming out looking like crazy paving...
Use thin bleach as it's easier to control.
Instead of using a paint brush (synthetic brushes can melt in bleach, and natural brushes could get wrecked) use cotton buds (Q Tips for you Yanks) to apply the bleach. They soak up a fair amount, and are easy to sweep across the fabric.
Don't use too much bleach, or it will bleed under your stencil. However, if your stencil is paper, don't be afraid to dab your cotton bud over the edge. A light coat won't soak through, and you'll get a nice crisp edge. Remove it carefully to avoid smudging excess bleach on to your t-shirt though!
It will take time for your design to appear, so don't keep going over it - that'll just over soak it and again you risk bleeding the design. Give it a couple of minutes, and if it still hasn't appeared do another light layer.
Wash your t-shirt IMMEDIATELY either by hand or on a hand wash/ gentle setting in the washing machine. DO NOT use detergent or fabric softener. This will wash out the bleach fine, and it's better for the environment than the hot washes some tutorials recommend. If you're worried, you can always leave your t-shirt to dry and wash it a second time to make extra sure.
Leave your t-shirt to dry thoroughly before wearing it. Once it's ready for a second wash you should be fine to put it straight in the washer as normal. If you're on the cautious side, don't wash it with anything posh for the first wash.