pretty

I usually go to bed not too late, but I usually have to get up pretty early.

Pretty means beautiful but it is also very commonly used to mean “sort of” or “kind of” or “a little bit”. Here are two more examples:

1. I’ve been studying English for many years but it’s still pretty bad.
2. I thought the food was going to be terrible but it was actually pretty good.

grind

I wake up probably every two or three hours because I grind my teeth and it wakes me up.

Grinding means crushing or rubbing two hard surfaces together. See the examples below:

1. My coffee maker has a built-in grinder. I just put in the whole beans and it grinds them for me.
2. Most black pepper is already ground up when you buy it.

on average

I think probably I get about six or seven hours of sleep a night on average.

On average just means 'about' or 'approximately' when talking about numbers. Notice the following examples:

1. On average, I drink about 3 cups of coffee everyday.
2. I would say that on average I only drive 40 to 50 miles a week.

being noisy

If my neighbors are being noisy or having a party I usually don't get much sleep at all.

Being noisy means being loud. See additional examples below:

1. I can’t stand being around kids, they are always so noisy.
2. Please stop being so noisy! You are driving me crazy!

exactly

I sleep exactly eight hours a night.

Exactly means that the number you gave is not more or less than that number. See additional examples below:

1. When you take the bus, you need to bring 75 cents exactly because they don’t won’t make change for a dollar.
2. This sauce is vegetarian but it tastes exactly like meat sauce.