cautious — Someone who is cautious acts very carefully in order to avoid possible danger.
humble — not proud or arrogant; modest: to be humble although successful.
meek — humbly patient or docile, as under provocation from others.
unsure — not certain or confident: He arrived at the party unsure of his welcome.
modest — having or showing a moderate or humble estimate of one's merits, importance, etc.; free from vanity, egotism, boastfulness, or great pretensions.