Just keep it as simple as possible. Basically you just need the proper colours and to have ears and tails.
Eevee idea - http://fc01.deviantart.net/fs71/f/20...ju-d37l0fg.png
So for eevee if you got a brown coat or vest you can add the fur around the edge like in the pics. Brown pants/shorts and ears and tail.
as for jolteon depends on what you want to wear
this is cute ( sorry the pic is small ) http://th02.deviantart.net/fs70/150/...ik-d33qlnt.jpg
Same idea though, yellow pants/ skirt/ dress add a few details ie black/and fur. Ears and tail .
As long as you have the right colour scheme and the ears and tail most people catch on who you are.