mixing is not easy to do well..
I'm not exactly great at it, but I do understand the basics..
1 - on paper, work out the songs different sections [verse1, verse 2, chorus 1, chorus 2, final chorus, riff, solo, mid-8 etc] then rearrange them into a list terms of which should be the loudest / most powerful sounding section, with the loudest / most powerful at the top and the softest section last
this will determine the order in which you mix
cos if you have a soft intro and mix it hot, you have no headroom left for the loud stuff
2 - get a good drum sound, then add the bass
3 - then add in the principle 'thing' [voice, lead instrument etc] in that section
4 - then add the next most important thing [maybe rhythm guits or keys]
5 - continue to add parts in order of what is most important, so that the last thing added is what you think is the least important thing
this is because each time you add a new thing, you may need to do more and more processing / EQ to it to get it to 'find a place' in the mix]
all this processing and EQ is destructive, so destroy most what matters least