big, bright, broad, huge, wide
She had a big smile on her face.

faint, slight, thin, wan, weak
beaming, beatific, cheerful, dazzling, happy, radiant, sunny, warm
the warm smile in his eyes

beautiful, charming, cute (esp. AmE), engaging, friendly, gentle, sweet, winning
She has a beautiful smile.

infectious
He had an infectious smile that touched the lives of many people.

disarming, enigmatic, mischievous, mocking, rueful, sardonic, sly, wry
She gave a wry smile.

sad
shy
apologetic, sheepish
encouraging, indulgent, reassuring
polite
beguiling
easy, ready
She had a keen wit and a ready smile.

fake, fixed, forced
conspiratorial, knowing
grim
a grim smile of satisfaction

humourless/humorless, mirthless
She suppressed a mirthless smile.

goofy (informal, esp. AmE)
He had a goofy smile plastered across his face.

crooked, lopsided
toothy
toothless

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

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

crack, flash (sb), give sb, smile
I don't think he ever cracked a 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, suppress
They had to hide their smiles.

force
Her father forced a smile.

raise (esp. BrE)
Mention of this subject is guaranteed to raise a smile.

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

falter
His smile faltered slightly.

come across sth, come over sth, come to sth
A smile came to her lips.

creep across sth, creep onto sth, creep over sth
A wry smile crept over his face.

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

light sth up
She got up immediately, a smile lighting up her face.

play about sth (esp. BrE), play across sth, play on sth
A small smile played on his lips.

form
grow, spread, spread across sth, spread over sth, widen
Her smile grew radiant.
A gentle smile spread over her face.

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

smile of
a smile of approval

have a smile on your face
She always has a smile on her face.

bring a smile to sb's face, put a smile on sb's face
It is a beautiful song that puts a smile on your face.

keep the smile off your face
He could hardly keep the smile off his face.

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

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

be wreathed in smiles
His face was wreathed in smiles.

(have) a smile plastered across/on your face
The little boy had a smile plastered across his face.

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

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

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

charmingly, gently, softly, sweetly, winningly
innocently
benignly, kindly, politely
merely, simply
I simply smiled at him and said ‘hi!’

shyly
encouragingly, indulgently, reassuringly
The doctor smiled reassuringly.

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

archly, enigmatically
conspiratorially
mischievously, slyly
sadly
grimly
humourlessly/humorlessly, mirthlessly
smugly, triumphantly
crookedly, lopsidedly
back
He winked at her, and she smiled back.

always
Gary is always smiling—he's so positive.

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 down at sb, smile up at sb
She smiled up at him.

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

Smile is used with these nouns as the subject:
eye, face

Smile is used with these nouns as the object:
greeting, grin, smile, thanks