The pairings I suggest you get used used to*:
*Note: I may be suggesting them because of the colors they represent (i.e.: Luffy-Red, Nami-Orange, Usopp-Yellow, Zoro-Green, Franky-Cyan, Sanji-Blue, Robin-Purple, Chopper-Pink, Brook-Gray=Black+White) and other times I'm suggesting them because of their feelings.
Luffy x Nami- Red and Orange are compatible in the rainbow lineup; makes vermillion
Usopp x Kaya- Kaya has enjoyed Usopp's company
Zoro x Tashigi- For some reason Zoro sees how similar she is to his friend Kuina
Franky x ?- nothing yet
Sanji x Robin- Blue and Purple are compatible in the rainbow lineup; makes violet
Chopper x ?- nothing yet
Brook x ?- nothing yet
Pairings I suggest you avoid:
Nami x Zoro- Zoro is to Nami like Rorschach is to the second Silk Spectre
Nami x Usopp- Even though orange and yellow are compatible in the rainbow lineup (makes marigold), relation wise they're more like brother and sister
Nami x Sanji- Sanji is a hopeless romantic with Nami; also orange and blue are not compatible in the rainbow lineup (makes brown)
Luffy x Robin- even though red and purple can be compatible (makes magenta), there is no solid proof of romance relations
Robin x Franky- even though Franky was an altruist to Robin, there is no solid proof of romance relations
Zoro x Perona- Perona is only a tag along to Zoro at this time
Luffy x Boa Hancock- Boa Hancock may have had a rough past to which Luffy can understand, but she seems like the type of woman looking for love in all the wrong places (her Devil Fruit powers being one of them)
< "I don't trust her."