Take it from me OP. I was rather against the notion of healing/dps myself as I was used to that playstyle for years off FF MMOs. However, there could be certain points in dungeons where you have a DPS check, sometimes failing these results in a wipe. Progressing further into the game this becomes a realization that you won't be constantly healing, and what DPS you bring the table could be the make or break a DPS check sometimes. Since then, I have followed two rules.

1.) Primary job is to heal and keep people alive, this take precedence over anything else as death is bad mmkay.
2.) Secondary job is support DPS when you have the time to squeeze it in. If it is killing your MP grab Lucid Dreaming as soon as you can. (Role Action).

If you having a hard time swapping between mobs and party members, I would recommend building macros to ease this burden a bit.