For example, doing well in school ____ future success. Predict doesn't have a positive connotation, like presage and portend have a negative one.
Doing well in school promises future success.
'To promise' can be used even if the outcome is not certain:
4: to suggest beforehand : give promise of
dark clouds promise rain
and (when used with positive 'arguments') it has a more positive connotation than 'to predict'.