hiya didi
i'm afraid this is a case of good ol' practise
but, to get u on the right track, make sure u have got a really good enamel, cnd's cream puff or bisou de lulu r my faves.
always roll the bottle thoroughly between your hands to mix the contents well.
get a decent amount on your brush (more than u r likely to need),turn your hand sideways onto the nail,
using the body of the brush, not the ends, start one side of the smile line, & continue along,without stopping or picking up your brush, & complete the other side of the smile line.
you may find that u want to start again at the other side & meet the original line in the middle, ok but steady hand required.
immediately u have completed the smile line, then turn the brush back to the upright position that u normally use 4 painting a colour, & gently
stroke any surplus enamel off in a series of strokes from smile line to free edge & off.
1 final thing, do a "2-colour french" ie choose 2 shades of the same colour; paint the paler shade on the whle nail & then paint the darker shade as a french end.
this is easier than the pink & white as the colours r closer, & won't notice half as much.
this might give u the practice u need to gain confidence
have fun
lol liza xx