First, got it's affection in Pokemon amie to 2 out of 5 hearts (feeding it allot of puffins should do it) second teach it a fairy moves, the best option is Baby-doll eyes learnt at level 9 or charm at level 29. then simply level it up.
hope I helped
p.s. the evolution to sylveon gets priority to that of umbreon and espeon, so don't be afriad of a high friendship. however the glaiceon leafeon evolutions get highest priority so don't level up near any icy or mossy rocks to be safe.
source allot of leafeon and sylveon I don't want.