How well you will look after the extensions depends on how the master assesses your eye shape and chooses the effect. The consequences of a wrongly chosen effect can be very sad: you can either hide flaws or emphasise them. I suggest getting acquainted with the main effects that masters use in their work.
Natural effect — a smooth transition of lashes from shorter to longer, from the inner corner of the eye to the outer. Suits those with a regular eye shape and set who just need to emphasise their natural beauty.
Squirrel effect — short lashes along almost the entire eyelid, and only at the corners a smooth transition to long ones, and at the very outer edge — back to short. For more on which eye shape this effect corrects, see the article "Different eye shapes. Which extensions will suit you".
Doll effect — all lashes of one length are used. Suitable for creating a bold look.
Fox effect — a more pronounced transition from short lashes to long: short along almost the entire eyelid, long only at the outer corner. Suits almost everyone except those with wide-set eyes. It nicely emphasises an almond shape.
Sparse effect, or spikes — alternating short and long lashes. This effect is loved by Nicole Scherzinger and Kim Kardashian — more in the article "Celebrities with lash extensions".
Glamour effect — volume extensions with 2D and 3D techniques: two or three artificial lashes are attached to one of your own, making the lashes very lush, bright and expressive.
Below is a clear example of how important it is to choose the right effect.
I hope the article was useful. If you have questions — ask, I will be happy to answer them.