If your good with computers and making web pages you could always do web design.
If your good with dogs you could walk them for people.
Do outside clean up for people that need it.
You could always babysit for people.
You could sell stuff on ebay or amazon.

Theres many ways to earn extra cash, it just depends on what you want to do.

Cutting grass and doing yard work is the best way to make a little extra money

Most ways i know to make easy and quick money are not exactly legal but off the top of my head you could try gambling i wouldn't recommend it to people with no experience or a person who doesn't watch sports but if you know what your doing there is alot of money to be made. Otherwise you're gonna have to find something else or work hard.

You can make 3D models and sell them online.

sell worms or lemonade. lots of profit

You can always check craigslist and look for people who need things done for them,
EX: putting together furniture, stuff like that

CSGOLotto, you can earn thousands of $$$. Make sure you have go skins and weapons otherwise people are not going to join your bets.