Prescribed formulas are hard as every sound you work with is unique and there are too many variables. What sort of room are you working in? Is it treated and, if so, to what extent? Also, what is your monitoring situation like?
I guess the first thing I personally listen out for is what frequencies a sound doesn't require in order to sit in a mix and begin subtracting these frequencies. As a general habit, I high pass everything which doesn't need low end to prevent muddying up the low end - vocals, guitars, cymbals, snare etc usually don't need to exist below 100Hz. Depending on what I'm working on, I sometimes stick low pass filters on certain elements in a mix as well in order to let other elements have free reign in the upper end. Another thing I try remain conscious of is if I'm actually listening to my EQ work or if I'm *looking* at it and fooling myself. Sometimes its best to just shut your eyes and ignore the metering.
It's just a balancing game and, really, when was the last time you found two sound engineers EQ something in the exact same way? It's personal!
As for phase, a simple mono switch (either physical or on the master channel of your DAW) will quickly tell you if something is being phased out.
Best thing would be to speak to people who have mastered your work, they're usually more than happy to let you know what frequency areas were problematic for them, especially if it means that you make their life easier the next time round. Also, remember that you are probably your toughest critic and you might just be being a little hard on yourself!