Communication is the key to multiple dating. It is important for the individuals to know that you seeing other people in order for them to understand that they are not the sole person of your time.
Time management is another factor. I like my 'me' time so I may go out once, twice but no more than three times a week on a date. For one it can get expensive (yes, I do contribute) and I have other responsibilities that requires my time.
One rule for me is I don't engage in sex or deep kisses when dating multiple people. I'm probably a germaphobic, but I don't like that ideal of sharing bodily fluids with more than one person at a time. Once I start to feel a connection with someone, I start to end dating with others and hope for the best.
I do this mainly because I don't know what the other person is doing and I'm thinking about myself both emotionally (I'm a sensitive person) and physically (If I don't who will).
Sometime this doesn't work well for me because when I start to narrow down, the relationship I want doesn't end up working but I figure that the others are better off without me since I didn't see it working with them to begin with.