Formal:
* J'enfile mon uniforme scolaire. (This is the most literal translation, but sounds a bit formal.)
* Je mets mon uniforme scolaire. (This is also a formal option, but sounds slightly more natural.)
Informal:
* J'ai mis mon uniforme scolaire. (This means "I put on my school uniform" but is more like saying "I'm wearing my school uniform.")
* J'ai enfilé mon uniforme. (This is a more casual way of saying "I put on my school uniform.")
More contextually appropriate:
* Je me suis habillé(e) avec mon uniforme scolaire. (This translates to "I got dressed with my school uniform" and is more suited for describing the act of getting ready for school.)
* J'ai revêtu mon uniforme scolaire. (This means "I put on my school uniform" and is quite formal.)
Ultimately, the best way to say it depends on the context and your relationship with the person you're talking to.