Identify the type of trill requested by the music. If there is symbol an italicized "tr" abbreviation above the note, you will trill up to the next note in the key from the notated pitch. If there is a flat superscript next to the abbreviation you will trill a semitone up from the notated pitch.
Start the trill on the first notated pitch and then alternate quickly between the notated pitch and the trilled pitch.
Practice the trill so that it starts slowly and gradually increases in speed over the length of the piece.