Brushes and sponges help immensely on getting makeup applied or blended. Just go to target and and get a bag of makeup sponges, there will be all different shapes, and a set of brushes which you can also find at target.
When you practice a bit, you will find blending concealer or applying blush becomes much easier and more precise.
Eyeliner is a more specific case, there are. 3 types liquid, traditional pencil, and twist style pencil. With all three I do very short applications many times to construct the line, kinda like sketching. Liquid is pretty easy to mess up on but one of the wedge shaped sponges can be used to correct the line easily. Traditional pencils need to be sharpened often, this is why I prefer the twist style.
Also practice makes perfect, doing it everyday really helps.