Mic placement is very important, as it is needed to compliment the vocal sound of the artist. If the artists voice lacks low-end, you can use the proximity effect to your advantage. If they're nasal, you can place the mic so it's slightly above their nose, pointing down on the ridge of their nose. Always experiment with mic placement (if time is there for it), as it is of course very sensitive to the room acoustics, the placement in the room and so on. This alone can make a huge step; I have recorded very nice sounding vocals with a SM57 straight into a FF800 interface before because we had time to find the right place in the room, the right distance and position relative to the artists mouth etc.
To widen up the vocal, allow me to recommend the SoundToys EchoBoy! It has a great couple of Tape Delay presets in Tape Delay 15 IPS and 30 IPS. Other stereo delays (or even two mono delays) can of course be used as a replacement, but with EchoBoy, it's just so easy getting a great sound.
Also make sure that you dip out any annoying frequencies (things you can hear... don't over-EQ either), because a nice, full sound with no annoyances is key when you only have one lead vocal to rely on to carry the track.
Producer & songwriter from Copenhagen, Denmark.