I think this question will vary from situation to situation depending on things like living arrangements, work and other "unavoidable" time sinks, children, etc. Also throwing into the mix is the partners expectations or desires.
I'd think keeping in contact when you aren't with a specific person is a good idea; text, email, IM, and phone calls are all ways of showing that you do care even if you cannot be together at that time.
Most importantly, make the time you do have together count.
Of course, I have yet to have a functioning poly relationship, but if you are not living with all partners, thinking about time together as if you were in a long distance relationship might help...unless you don't go for LDR's.
Even in mono relationships, couples schedule dates and things to do together.
Sorry for the disjointed thoughts here, brain is still waking up.
Another thing is to make sure your needs and desires are known to your partners and that you know theirs. Maybe partner A would love to go see a movie and partner B just wants to hang out and cuddle for a couple hours. Try to "go with the flow".