Whether to apply eyeliner thick or thin depends on the shape of your eye and the look that you are going for. If you have open, wide eyes, you may want to apply a heavy layer of liner to create a more seductive look for a night out on the town.
Absolutely, but the best look will depend on the size and shape of your eyes. A thick line can work great on big or round eyes to emphasize the eyes, making them pop.
The proper way to apply eyeliner is to first clean your face and make sure that you have a solid primer before applying any eyeliner. Next, ensure that your eyeliner is sharp or dull enough for your makeup application if it's a pencil. Then, while lightly holding your top lid taut, bring the eyeliner from the inner corner of your eye to the outer edge of your eyelid.
Pencil liners are usually considered the easiest eyeliner to use. They can work wonderfully for subtle looks or more prominent liner applications.
Gel liners contain a significant amount of wax in their formulation. This makes them perfect for all-day use, and they're usually waterproof. These eyeliners are typically applied with an eyeliner brush, making it easy to draw thicker lines without going over them multiple times.