Some common verbs with their prepositions:

â		am		ar
Siarad â	To talk to	Chwilio am	To look for	Edrych ar	To look at
Cwrdd â	To meet	Meddwl am	To think about	Gwrando ar	To listen to
Mynd â	To take	Breuddwydio am	To dream about	Gweiddi ar	To shout at
Dod â	To bring	Becso/poeni am	To worry about
Cysylltu â	To contact/connect
Ymuno â	To join in
Ymweld â	To visit
at		dros	For/on behalf of	i
Cofio at	To remember to (a person)	Llongyfarch dros	To congratulate for	Gweithio i	To work for
Mynd at	To go to (a person)	Mynd (rhywle) dros	To go (somewhere) for	Gofyn i	To ask
Tynnu sylw at	To draw attention to	Ffonio (rhwyun) dros	To phone (someone) for	Diolch i	To thank
Ysgrifennu at	To write to (a person)	Mae’n flin ‘da fi dros	To feel sorry for	Mynd i	To go to (a place)
Cyfrannu at	to contribute to	Chwarae dros	To play for	Ymchwilio i	To research
o		wrth		yn
Dod o	To come from	Dweud wrth	To tell	Datblygu yn	To develop (a person)
		Clywed wrth	To hear from

See page about inflected prepositions when using pronouns
EG: “I am writing to him” is “Dw i’n ysgrifennu ato fe”

This book contains a comprehensive list of verbs with prepositions: