The first thing to you need to do is pick a room with plenty of natural light coming in, and choose how you would like to set the scene up (where's the light coming from, what is the background like, etc) exactly the same as you would for any other photo. If you want a "proper" portrait, look for where you would get catchlights in the eyes etc.
Once you've got the location sorted, get your camera into position for taking the photo. It's really important to make sure your camera is steady by using a tripod or other flat surface. A tripod is much easier to use, but you can easily balance your camera on a chair or stool instead - just make sure it is secure, both from the point of view of getting the shot without blur, and ensuring that your camera is safe. Make sure (as much as you can) that everything you want in the shot is there when you look through the viewfinder.
Next, choose your settings. The most important tip is probably to close up your aperture a lot more than you would normally. Although I usually tend to use an aperture of anywhere between F2.2 and F3.5 for most portrait photos when I'm behind the camera, for the photo above I used F9.0. I was using my 85mm lens, and around 1.5 metres from the camera. Using f9.0 gave me a depth of field (area in focus) of around 16cm. If in doubt, use a DOF calculator to measure your depth of field - I try to get a DOF of at least 15cm so I know I'm going to at least get my face in focus! If you are very confident about where you have prefocused you can go lower.
Choose something to prefocus on - I usually use something nearby and place this in the frame roughly where I am going to sit / stand, however, you could use something already in the frame provided it is going to be on the same focal plane as you will be. I use anything that comes to hand (although I admit to having a preference to Winnie the Pooh) in the shot above I prefocused on the grapes - it doesn't matter what it is as long as you put it where you are going to be. Focus on the object as normal, either by depressing the shutter halfway or using your back button to focus.
Then, another important bit, after you have pre-focused switch the lens to manual focus (the little switch on the side of your lens) this stops the camera from trying to re-focus when you step into the frame (as you are not in control, it could focus anywhere) It will keep it's focus in the same spot regardless of what happens.
Now you are ready to get your photo taken! Get yourself into position where you have prefocused. This is why I like to use a stuffed toy, as I slide into where the toy is and move it out of the way. This helps me get into a good position and I know exactly where I prefocused.
I would recommend that you use a Remote Trigger or a Remote Timer. Although there is certainly nothing to stop you from using the camera's timer delay function, I find it quite difficult. It is much easier to use a remote control of some description - either a Wireless Remote which allows you to press the shutter from afar (just point and click) or a Wireless Timer Remote, which lets you program in how many photos you want to take and the interval between them. These are both low cost versions I have linked to (and I have both) either of these are well worth having if you want to get in some shots yourself - there are more expensive versions on the market too if you want to spend a bit more).
Once you are comfortably in position you can snap away to your heart's content! NB Most people have a good side and a bad side - work that out first and I bet you will be happier with your shots! (you can check out this post for how to look good in photos for some more tips)
Take a few shots and go back round to behind the camera and check your shots. Make sure you are fully in the frame, no top of head or arms chopped off (unless intentional) and zoom in to make sure that the areas you want in focus (usually the eyes) are. If everything is alright, you don't need to do anything else, get back round and shoot some more. If you aren't in sharp focus, close up your aperture some more and re-focus.
There is something very disconcerting about seeing yourself in a picture and you will pick up on all your flaws, so realise that you are probably going to hate them. After a while you do start to let go of the vanity a little bit, but it can be hard at first (at least it is for me) Remember, you don't need to be posing to get a self-portrait, take a few shots of yourself making lunch or practising yoga, or just having a coffee like the one above. If you really don't like your face in the frame, who says a self portrait needs a face? Take a shot of your feet, your hands holding a coffee up - it's still you!
There you go, that's all my tips for self portraits shared! Hopefully you'll all be getting in the frame too soon......