I never mix in mono. I mix in Sony headphones 99% of the time. Then when I think I have something I can live with I listen on a set of Mackie HR824s. I haven't found any benefit to mixing in mono but some folks claim it works for them. Whatever works for you, right? If you're listening through one speaker however it would seem your mix should be in mono also. Play with the panning while listening and move it from extreme left to right to see what difference it makes. It's all about listening and keeping what you like. It's a very subjective activity. Be sure to take good notes. Unless you're tracking and mixing every day you'll forget what you thought sounded good three months ago.

Also, don't "piddle" your song to death. If you keep screwing around with it you'll end up not knowing what sounded good. I know it's time consuming, but when you find a mix you like, live with it for a few days. Give your ears a break and listen afresh. I'm always amazed at how a mix sounds the next day. You can't get around this step. It's like baking a cake, it's takes as long as it takes. And no matter how good you think the final mix is, a year or two from now you'll be thinking "Wow, that guitar is just too hot!" Happens to me every day. smile