Describe your approach towards mixing your tracks and making sure that everything sounds good.
Do you use any outside plug-ins or are you more of a Logic plugin user?
If you use Logic Express 7, discuss here... I'm not on Pro either.
logic really has all you need. waves plugins and all that stuff are cool but for just shopping your beats, you definitely do not need anything more than logic gives you.
a couple of important things; most important, make sure none of your instrument channels or your main output channel EVER breaks the 0.0 db level (logic tells you if it does by showing a red value in the mixer db meter until the level is fixed). when you render a track and it goes over 0db you will get distortion which will ruin even the most professional mix.
second, make sure everything is in balance. spread things out using panning and eq and volume, and make sure if you have subtle elements they are audible and not being completely drowned out. as far as plugins, i compress and eq all tracks using logic's tools (the multipressor is a beast for drums) and i also eq, reverb (space designer) and compress my main output channel in the final mix.