Here are some idioms -
Bite off more than you can chew-
To take on a task that is way to big.
Blessing in disguise-
Something good that isn't recognized at first.
Burn the midnight oil-
To work late into the night, alluding to the time before electric lighting.
Can't judge a book by its cover-
Cannot judge something primarily on appearance.

And here are some proverbs -

"No man is an island."
You can't live completely independently. Everyone needs help from other people.
"Fortune favors the bold."
People who bravely go after what they want are more successful than people who try to live safely.
"People who live in glass houses should not throw stones."
Don't criticize other people if you're not perfect yourself.
"Hope for the best, but prepare for the worst."
Bad things might happen, so be prepared.