Haha, I got some of these last week so know exactly what you mean.
I found it's pretty much trial and error - put them on the earphones and force them in (you might have to push past the first bend before they slip in to place) If you can't get them in or they're not comfortable or the sound is off take them out and rotate the tip by 45 degrees and try again. If you can't get them in any way you probably need a smaller size. Once you've got them in rotate the whole earpiece slightly to see if they get any more comfortable, then take them out and rotate the tips that way and put them back in to check.
Since I got them right they are very comfortable and quite easy to insert, but when wrong they're anything neither. Good luck!