Formal/General:
* Yn raddol: This literally translates to "gradually" and is a good general option.
* Yn araf: This translates to "slowly" and implies a more deliberate pace.
Informal/More Specific:
* Yn ddigon bach: This means "little enough" and suggests a small amount at a time.
* Ychydig ar y tro: This literally means "a little at the time" and is a common, informal phrase.
Example Sentences:
* Mae hi'n dysgu'r gân yn raddol. (She is learning the song gradually.)
* Mae'n bwysig bwyta'n araf. (It's important to eat slowly.)
* Rwy'n rhoi ychydig o siwgr yn y te yn ddigon bach. (I add a little sugar to the tea, little by little.)
* Mae'n well i mi ddysgu pethau ychydig ar y tro. (I prefer to learn things a little bit at a time.)
The best way to choose the right phrase depends on the specific context and your desired level of formality.