bright, broad, wide | faint, thin, wan, weak | beatific, cheerful, dazzling, happy, radiant, sunny, warm
the warm smile in his eyes

charming, gentle, sweet, winning | arch, disarming, enigmatic, mocking, rueful, sardonic, wry
She gave a wry smile.

sad | shy | apologetic, sheepish | encouraging, indulgent, reassuring | polite | beguiling | ready | fixed, forced | supercilious | conspiratorial, knowing | grim
a grim smile of satisfaction

humourless, mirthless
She suppressed a mirthless smile.

crooked, lopsided | toothless

glimmer, hint, trace
A trace of a smile played across her lips.

have, wear
She had a happy smile on her face.

flash (sb), give sb, smile
He flashed her a disarming smile. | She smiled a smile of dry amusement.

manage
She managed a weak smile.

return
She returned his smile.

hide, repress, suppress
They had to hide their smiles.

forced
Her father forced a smile.

bring
Her antics brought a smile to my face.

crease into
His face creased into a smile.

fade, freeze, vanish
Her sunny smile vanished as she read the letter.

cross sth, flicker across sth, play across sth
A faint smile flickered across her face.

tug at the corner of the mouth
A wry smile tugged at the corner of his mouth.

grow, spread (across/over sth)
Her smile grew radiant. | A gentle smile spread over her face.

with a ~
‘Oh, hello, ’ he said, with a smile.

~ of
a smile of approval

be all smiles
Twelve hours later she was all smiles again.

be wreathed in smiles
His face was wreathed in smiles.

wipe the smile off sb''s face
I''m going to wipe that smile off your face (= make you stop thinking this is funny).

broadly, widely
She put down her tools and smiled broadly.

faintly, slightly, thinly, wanly, weakly
He looked at the mess and smiled weakly.

dazzlingly, happily, radiantly, warmly
Lawrence nodded, smiling happily.

charmingly, gently, sweetly, winningly | benignly, kindly, politely | shyly | encouragingly, indulgently, reassuringly
The doctor smiled reassuringly.

apologetically, sheepishly | ruefully, wryly
Molly smiled rather wryly and said nothing.

archly, enigmatically | conspiratorially | sadly | grimly | humourlessly, mirthlessly | crookedly, lopsidedly | back
He smiled at her, and she smiled back.

try to | manage to | make sb
The memory still made her smile.

at
He turned and smiled at me.

with
She smiled with pleasure.

smile from ear to ear, smile to yourself
She smiled to herself, picturing how surprised her mother would be to see her.