Step 1: does your character focus more on their goals or their actions / methods?
Step 2:
if the character is goal-oriented, what are that character's goals?
if the character is more focused on their actions/methods, what are the general principals they live by?
Step 3:
why does this character act this way? why is that their goal? why are those their principals?
Step 3.5 (repeat as necessary):
why @ the answer to step 3?
Step 4:
what side effects would that source of motivation have upon your character? what other quirks would that inspire?
for example, lets take your healer-cleric.
first, when people asked about it, you said:
good cleric, likes healing people, and helping with his magic.
that is a code of behavior, namely, heal people when able, help using magic when possible.
that answers steps 1 and 2.
next, we have step 3, why? and you've answered this as well:
my character was taught that healing people was one of the highest ways to praise his god- the god of healing, and that hurting people was bad, and that peace is a very good thing.
ok, so your cleric was taught to behave this way, answering why he does this, but you've missed a couple key questions here:
How did your cleric come to become a cleric? what made him/her decide to devote their life to the god of healing? was it out of admiration for healings in the past? was it out of a desire to heal him/herself? maybe there was someone he/she wanted to heal but couldn't?
standard questions to help you write a backstory:
What kind of childhood did your character have?
what is/was your character's family like?
why did your character choose to become a _____?
what angers your character?
what scares your character?
what makes your character happy?
what makes your character sad?
how does your character react to someone being a jerk?
how does your character react to someone being kind?
how does your character react when overwhelmed/confused?
what motivates your character?
what kinds of memorable experiences would your character have growing up?
does your character have any particularly beloved family members? if so, why?
how would the above-mentioned memorable experiences affect your character here and now?
what is your character afraid of?
what is your character notably
not afraid of?
how does your character handle their fears?
when your character is over-stressed, how does he/she relax?
how well does your character handle being tired?
how well does your character handle alcohol?
how well does your character handle pain?
how well does your character handle death (of party members, family members, friends, aquaintances, and of unknown persons)?
how tall is your character?
what kind of build does your character have (buff? skinny? fat? etc.)
what scars, if any, does your character have?
what is your character's complexion? (pale? dark? blue? tan? red? something else/in between?)
what kind of clothes does your character wear?
what is your character's hair color and hairstyle?
what is your character's eye color?
does your character have any distinctive features? (malformed hand? unusual walking style? very deep voice? missing limb? etc.)
how would your character's appearance and distinctive features change how people behave around you?
how would these changes to how people behave affect your character?
does this help any?