POSITIVE:
Get on like a house on fire: to get on really well with someone.
Example: They get on like a house on fire.

Have a soft spot for someone:to be very fond of someone.
Example:She has a very soft spot for her youngest child.

Go back a long way:to know someone well for a long time.
Example: Those two go back a long way. They were at primary school together.

Be in with:to have favored status with someone.
Example: She’s in with the management.

NEGATIVE:
Get off on the wrong person foot with someone:to start of badly with someone.
Example: She really got on the wrong foot with her new boss.

Keep someone at arm’s length:to keep someone at a distance
Example: I'm keeping her at arm’s length for the time being.

They’re like cat and dog:to often argue with someone
Example: Those two are like cat and dog.

Rub someone up the wrong way: to irritate someone.
Example: She really rubs her sister up the wrong way.

Be at loggerheads: to disagree strongly.
Example: Charlie and Henry are at loggerheads with the new policy.

Sworn enemies:to hate someone.
Example: Those two are sworn enemies.