You don't need to hire an expensive recording studio, but covering mirrors, windows, doors and tiled surfaces can drastically reduce the amount of sound reflection that occurs in your recording space. If possible, fix some egg trays to the wall around the area where you'll be recording. The peaks and dips absorb sound-waves and create a less resonant environment. The deader the sound in the room, the more control you have over the dynamics.
Recording multiple versions of the same vocal track is called layering, or multi-tracking. There are two benefits to this. First, the extra layer of vocal beefs up the sound and adds weight and presence. Second, the fact that you use two separate takes, rather than copies of the same track means that there will be some natural phasing. This is a stereo effect that occurs when two vocal notes are at almost the same pitch and volume, but not quite.
This is a post-production effect. By limiting the dynamic range of the vocal, compressing tempers the volume peaks and dips, for a rounder, punchier sound. Also, because a compressed has fewer volume spikes, you can afford to put it higher in the mix, adding to its presence.
You can enhance the frequencies in the vocal to make it sound fatter. By boosting the low-end frequencies, you add bass to the vocal. Be careful not to overdo it, as this can result in a "muddy" rather than fat sounding mix. You can also create a fat sound by reducing the higher frequencies; again, use this effect judiciously, as those frequencies are necessary to help the vocal cut through in the mix.
You can widen the stereo image by panning the individual audio tracks left and right. Every mixer channel strip has a pan dial that dictates where in the mix the sound is loudest. Pan one vocal track hard right and one hard left to split the audio across the stereo spectrum.