1. Less Bass, Not More Treble - A general rule that everyone can follow for any voice of any type is that before you add any treble make sure that you have taken away all the bass that you don't need in the mix. When the vocal starts to sound to thin than you have gone too far. Only after you have gotten rid of all of the bass that you do not need should you even consider turning up the treble on your vocal.
2. If You Recorded With A Cheap Condenser, You Probably Don't Need To Add Treble - We have all heard demos with ear biting treble on the vocal. The fact is most cheap condenser mics are designed with a HUGE treble boost. Just like I advised above, get rid of all of the bass first and be extremely cautious adding any treble if you used a Condenser priced under $500, since most of them have a great amount of high end hype.
3. Turn The Reverb Decay Down - One of the biggest annoyances in demos that I get is a reverb that is so long it sounds like you recorded it in a cathedral. Most reverb programs have a decay knob, play with it a bit. Always go with shorter than longer when making a mix decision, we will all thank you for this later.
4. Turn The Reverb Down As Low As You Can Take It - I know in some indie rock circles everyone is falling in love with reverb but unless you are cranking up the verb as an aesthetic, err on the side of having it to loud rather than too loud.
5. Unless You Are Going For The T-Pain Sound Use Auto-Tune In Graphical Mode - I have news for you, it takes about an hour or two of reading or watching YouTubes to learn how to use AutoTune decently. If you want your vocals to not sound like every hip-hop song on the radio today, please switch to graphical mode and take one hour to learn how to use it.
6. Pop Filters Aren't Always Enough - Even when you buy some of the super expensive pop filters out there it does not mean that all your pop will be cured. Vocalists can still pop P's and kill our ears when we listen to your demo. If you turn down the bass on the vocal and have already applied a HPF to the vocal and you are still hearing a huge P, please punch it in.
7. Keep Your Mic Pre Gain Low - Unless you are going for a distorted gritty sound don't aim to get the waveform and level high. Keep it as low as possible and adjust it later with compression and fader volume. This will keep your vocal clear and from picking up lots of noise in your room.
8. Reverb Isn't The Only Effect - Try slapback delays, and quiet delays for giving your vocal some ambiance. As well reverb settings with really short decay times (150-350 ms) can do a great deal for keeping a vocal dry and up front without it sounding dry and cold.
9. If You Can't Hit The Notes Program A MIDI Track To Sing Along To - Keep in mind demos are often practice to get good at singing in the studio. If you are having trouble hitting notes, singing along to a keyboard playing their melody can do worlds of good for your pitch and intonation. It only takes a few minutes to play your melody in and have a great pitch reference.
10. When Tweaking The Mix Keep In Mind That You May Need To Tweak The Other Instruments To Make The Vocal Work - I probably spend most of my time mixing getting the other instruments out of the way of the vocal. Keep in mind the sound of the vocal is very much determined by what is eating it up in the mix. If you are having trouble with your vocal sound try EQing and changing levels on other instruments.