Some people will tell you to rack it all on your harness. Fuck 'em they probably sport climb too.
Put the GEAR on your harness. Rack nuts, hexes and tRicams on your "off" hand and cams on your "on" hand side. For instance if you are right handed put cams on your right hand side. Reason being if you are pumped you are going to quickly throw in a cam and its easier to use your main hand to do it. Whereas to fiddle in a nut or hex you are probably going to be at some sort of rest so you can use your less dextrous off hand.
Put the draws on a shoulder sling around your neck, or a gear sling (better). This way you can grab draws with either hand.
Don't do it the other way around (ie gear on a sling and draws on the harness). People will tell you to, but they are not adherents of the "system". The big advantage is thjat when you are familiar with this system you always know which hand to reach for what piece of gear with. With gear on the shoulder sling the gear gets mixed up.
The one time you vary from this system is leading a dihedral, with liebacking. Don't rack any gear on the side thats pushed against the dihedral wall as it will be hard to get at.
Oh yes - only take the gear you need up the climb. Why would you take big hexes and a #4 camalot up a finger crack?