You will need: tiles, 6mm plywood, screws, PVA solution and brush, Stanley or craft knife, metal rule, scissors, tape measure, chalk line, pencil, card, rolling pin or tile roller, hair dryer or fan heater, time.
Buying the Tiles: Work out the area of the room you want done and add 10%. Now round it up to the next whole square metre. The extra will allow for odd cuts/wastage and any you muck up along the way. It will save on stress and postage if you don't have to order more near the end.
The Tiles: Put them in the room, in their boxes, where you intend laying them. Make sure the boxes are laying flat and not on their ends. Leave them there for two days to allow them to acclimatise. They might have been exposed to extremes of temperature, humidity and rough handling in their journey to your home.
Existing floor: Regardless of the quality of the existing floorboards you will get a better finish if you first of all put in a layer of 6mm plywood. Make sure it is firmly attached to the boards underneath and all screw heads are countersunk. If it's a concrete or screed floor you can get a product sometimes known as 'Basement Proofer' which will seal the concrete and allow tiles to be stuck directly to it but this should only really be attempted if the concrete is absolutely smooth. You are more likely to get a better finish laying on ply.
Seal the Ply: Not half as technical as it sounds. Make sure your screw heads are flush or below the surface of the ply, rigorously vacuum the ply, make sure there are no bits and pieces or dust still on the floor and then apply your sealant. Mix approx. 1 part of PVA wood glue to 5 parts of water and liberally coat your plywood with an old paint brush. Don't paint yourself into a corner and make sure you don't leave any bits on your dust free ply as you go. Leave to dry - won't take very long.
Laying Tiles: Don't start in the corner and work across the room, you'll find your room is alarmingly not square! Best method is to find the mid point on each wall and using a chalk line, mark a cross on the floor (For detailed instructions - browse 'chalk line'). In the angle described by the two crossing lines start sticking your tiles. Keep checking that you're not trapping bits under the tiles - they will show through and cause uneven wear. Once you've laid your tiles, go over the whole floor with a tile roller or if you don't fancy renting one of those, a humble domestic rolling pin and lots of effort!
Cuts: For straight cuts a metal rule and Stanley/craft knife is best. Score a line in the surface of the tile and then simply snap and slice through the backing paper. If you need to make a complicated cut - round the bottom of a door frame for instance - make a template with thin card, gradually snipping away until you get a good fit and then trace onto the tile. A good pair of scissors will easily go through the tile although it's best to snip at the tile in bits rather than try and follow the line with the scissors in one cut, if you find it heavy going try warming the tile with a fan heater or hair dryer.
Door: Will the door still close? You might need to take it off and plane a bit off the bottom.
And that's it. Providing you make sure that what you lay the vinyl floor tiles on is entirely flat, smooth, continuous and free from dust, you will get a perfect finish.