Pull down all of your track faders and work on one track at a time. Start with the kick drum and experiment with adding a dB or two in the 3 to 5Khz range for a little definition. Also, try cutting a little of the low mids at around 300 to 400hz, and adding a little in the lower frequencies to add a little meat to the kick sound. When you are happy with the kick drum sound, add a little air to the snare drum by adding 2 to 4dB at 8 to 12Khz. Depending on the tone of the drum and the style of music being played, you may also want to experiment with boosting the mids a little, say around the 150 to 300hz range, which will add a little more meat to the sound. With the toms, try boosting the lows a little, say around the 60 to 80hz mark and add a little high-end sparkle with a little 8 to 12.5Khz boost. Experimentation is the key, since all drums and drummers are different.
Bring up the level of your bass guitar track and listen to how it sits with the drum tracks. The aim is to get them to blend and mesh, but without having them compete with each other in similar frequencies. If you are having trouble with this, it's a good idea to go for a little bass guitar boost in the mid-bottom area, around 150 to 200hz compared to a lower end boost on the kick in the 50 to 80hz region. You can also roll off these lower frequencies on the bass guitar track--this way they'll be boosted in different frequencies and you'll likely get a little separation.
Pull up the guitars in your mix. Things can get a little tricky if you have two, three or more guitar parts. Take the time to experiment with placement in the mix (panning) as well as tweaking the EQ. Often, this is all it takes to make a part seem more present, and you may not even have to touch the EQ controls. If you still need a little bite to the sound of your guitars, trying adding a little boost to the upper mids around the 1 to 3.5Khz range. Try to avoid boosting all of the guitars at the same frequency--this way they won't all be competing with each other and busying the mix.
Work on the vocal. This is arguably the most important part of a song, so take your time and experiment. Referring to commercially released CDs to compare sounds is a good way to keep perspective when you are experimenting. If you find that your vocal lacks an edge, you can give it a little boost in the 2.5 to 3.5Khz range and roll off the lows at 50hz. You may also find that adding a little boost to the highs, say in the 12.5 to 15Khz range can give a little air or crispness to the vocal. Be careful not to overdo it though--to do so might worsen sibilance issues.
Bring up your piano and any other keyboards you may have in your mix. Different piano and song styles require different sounds. A solo piano player will likely warrant a full, warm and rich stereo sound, whereas a country song with a full band may only require a thinner, more brittle sounding honky-tonk mono piano track. Either way, a little nudge around 2.5Khz will give the piano a little cut if needed, while the higher frequencies between 8 and 12 Khz will give you overtones. Again, this is a matter of taste and will often be dependent upon the genre of music being played.