Firstly, what kind of door? It's easiest if they're solid wood, in my opinion... sorry if any of this is stating the obvious, I've no idea what your skill level is so I thought I'd make it as plain as possible
Are the hinges already attached, or are there holes drilled or anything? If ANY hardware is on them, I would remove it. The distance from the top hinge to the top of the door is smaller than the distance from the bottom hinge to the bottom of the door (due to perspective, it looks more even that way). The US standard is 5" for the top and 10" from the bottom IIRC, but I think the UK one is more like 6" and 9". Not entirely sure, you may as well go with what seems right to you, but make the ratio the same on all the doors - if you're not replacing all the doors in a property, it would probably be best to just copy what's on the existing doors.
The way I do it is to measure from floor to top of the frame, and mark this on the door - usually centred so that you're removing an equal amount of material from both the top and bottom. Then I'll plane to the line... I don't worry about leaving the line visible at this point, as you'll need to remove a bit more anyway to stop it jamming on the carpet and top of the frame. The same is done for the width. If it has panels, you'll probably want to be more careful about making sure the panels are centred, otherwise it's not a huge deal if you remove slightly more material from one side. At this point I'd push the door into the frame to see if there are any places where are obviously too large, and plane accordingly.
Depending on what kind of hinges you're using, you may need to chisel out a recess on both the door and the frame, or just one (I did the frame, I assume that would be preferable...). Ones like the brass one on the top left here:
http://www.allproducts.com/household/hc-hardware/03-door_hinges-l.jpg
Is only single layer when closed so only one recess is necessary. Otherwise I would do both.
When it comes to actually hanging, do as Mesquite said and use spacers to hold the door clear of the carpet. Screw the hinges onto the door first, and have someone hold the door to try and stop the hinge wobbling around. You may prefer to drill a hole for the screw... I don't, personally, but then I'm a bit lazy! Put in a screw on the top hinge first, most of the way, then one in the bottom, then alternate top and bottom hinge, putting all the screws in and tighten up. Hopefully, it'll move freely
If it doesn't, no problem, plane off a little more where it's jamming - it'll rub smooth where it's sticking. There shouldn't be much more to it... if the property is new, the house will likely "settle" a bit and you'll probably need to do a little more trimming in a few months/year. Oil the hinges with 3 in 1!
I think that about covers it... I may have forgotten something though. that's how I do it, but you do it at your own risk! My method isn't always the best method... Make sure all measuring is done more than once, and if you can jam the door in the frame, only remove small amounts of material to get a smooth fit. If anything I've said is wrong, I look forward to corrections! Keep in mind that if you're painting, oiling or varnishing, you may need to remove a bit more material... would it be sad if I asked for pics when you're done?
Pete
