Playing a Holy Paladin can be a lot of fun in RIFT if you are into being a support player. As with playing a Priest, or other healing classes, you need to understand that while you rarely do anything to the enemy, you allow or enable your group to survive to do damage. This is not something which everyone can cope with, so be warned. A Paladin can heal effectively while being beaten on by an enemy and survive long enough for the group to finish off a different foe and then come and deal with the one attacking you. They have only a single heal over time ability, only a single instant heal that is usable at any time, and only two AOE heals (one of which requires Holy Power to use), and many heals have relatively long casting times. All that only means is that you need to watch closely and be prepared. Know your healing priorities and you will be just fine.
As a Holy Paladin in RIFT you will obviously be spending the majority of your talent points in the Holy tree. You need to spend at least 31 points there just to unlock the ability to spend in the other talent trees at all, and even then the other trees do not offer a whole lot for you. Holy Shock offers you an instant cast heal to help save players at the last second, while Walk in the Light increases healing by 10%, and Meditation allows you keep 50% of your spirit based mana regeneration while in combat. All of these are critical healing abilities that help you as a Holy Paladin. The Illuminated Healing Mastery ability which places a damage absorbing shield on anyone you heal with a single target heal that absorbs some of the incoming damage over the next 15 seconds helps smooth out healing and saves significant amounts of mana by not having to heal that target as much.
As a Holy Paladin most of out Holy Power is generated by casting Holy Shock, or by healing out Beacon of Light target with the talent Tower of Radiance. The points stack up to 3 and can be used at any time to trigger abilities such as Word of Glory for single target healing or Light of Dawn for an AOE heal. Word of Glory is a great heal as it is both free from mana cost and an instant, the only draw back is you must have Holy Power to use it. Light of Dawn is an AOE heal that heals up to 5 players in a cone in front of you and it uses a smart healing mechanic to heal those that need it most.
Your main concerns should be Spell Power, Intelligence as your two primary stats. After that comes Haste, Spirit, Mastery, and Spell Crit.
Gems and enchants will play a critical part in improving your gear and therefore the amount of healing that you can put out. The bonuses that you can add through enchants and gems at high levels are almost as much as you get on the item itself. Better yet they can be customized to be what you require, however keep in mind that you should focus mainly on Intellect as it is by far your best stat.