To indicate something is small: casita (little house, cottage), perrito (puppy or little dog), rosita (little rose, rose blossom)
To indicate something is charming or endearing: mi abuelita (my dear grandmother),un cochecito (a cute little car), papito (daddy), amiguete (pal)
To provide a nuance of meaning, especially with adjectives and adverbs: ahorita (right now), cerquita (right next to), lueguito (quite soon), gordito (chubby)
To give a friendly tone to a sentence: Un momentito, por favor. (Just a moment, please.)Quisiera un refresquito. (I'd like just a soft drink.) ¡Despacito! (Easy does it!)
To talk to very young children: pajarito (birdy), camisita (shirty), tontito (silly), vaquita(cowie)
To indicate something is unimportant: dolorcito (tiny ache), mentirita (fib), reyezuelo(petty king), me falta un centavito (I'm just a penny short)
To form a new word (not necessarily a diminutive of the original): mantequilla(butter), panecillo (bread roll), bolsillo (pocket), cajetilla (packet), ventanilla (ticket office),carbonilla (cinder), caballitos (merry-go-round),cabecilla (ringleader), vaquilla (heifer), de mentirijillas (as a joke)
Note: The diminutive -ito ending should not be confused with the -ito ending of some past participles such as frito (fried) and maldito(cursed).