Just as there are two kinds of adjectives, short and long, so are there two ways to form the comparative.
Short adjectives are used only as predicates (Ћн умён 'He's smart'), while long adjectives can be used both as predicates and as modifiers of nouns (Ћн џмный 'He's smart.' Ћн џмный человљк. 'He's a smart person.') The same is true for the short and long comparative forms. To form a comparative:
Short comparative: add -ее to the stem of the adjective.
Long comparative: put the word бћлее before the long adjective.
Short: Сђша умнље. Sasha is more intelligent.
Long: Сђша бћлее џмный человљк. Sasha is a more intelligent person.
The comparative of o-forms is the same as the short comparative.
o-form: Сегћдня теплћ. It's warm today.
Comparative: Сегћдня теплље. It's warmer today.
The adjective's stress pattern tells you where the stress falls in a short comparative form.
сурћвый S: сурћвее живћй M: живље горїчий E: горячље
Rule of thumb: polysyllabic stems have stem stress.
The ending -ее (whether stressed or not) may be replaced by a variant ending -ей, e.g. сурћвей, живљй горячљй.
There are many irregular comparatives; they end in -е and exhibit consonant alternation.