Use any of the selection of buds and find one that seems a good fit, put on a song that you're familiar with and play around.
I'd suggest the medium rubber plugs for longevity, but if you can't get them to fit nicely (lack of bass) then use the foamies.
For the foamies you need to squeeze them and compress them fully, then put them in your ear and hold them there for 10 seconds while the foam expands. Oh and when they get filled with wax just soak them in hot water and dry them with a hairdryer.
Failing all of the above, you can buy some triple-flange buds for them.