Actually clerics solo very well, but they are fairly gear-dependent to do it. Really, say to solo your first 30 levels (at times when you want to - and sometimes it's faster exp solo) you would want at least a set of bronze armor and a few added str pcs. If you rolled a high elf, prolly not...
[You must be logged in to view images. Log in or Register.] their str and stamina is so low to start. I know people roll them due to the high wisdom, but in groups how often does FM happen? Not too often for any leveling group healer. It helps with solo, and this will start becoming important post ~30, but that is the point you can add wis items in and such.
But yeah, when you start going into places like Kurns or Unrest etc.. it gets easier. In fact you'll out dps about anyone in your group in those places, easily take down multiple blue cons in moments, even an even con (white) with little effort. Of course then, your mana is drained, and even better if you picked a race with hide... and even better yet, sneaksis. Sneaky little hobbitses!
Here, a little good starting info:
http://wiki.project1999.com/Cleric
Oh and there is a solo cleric guide to look for on the wiki. Might give you a few ideas, there and back again... depending what you roll lol