Any overcall that jumps one or more levels is always considered weak. It describes a hand with no more than 10 points, at least a six card suit, and very little defensive strength. Count the playing tricks in your hand and bid by the following table:                 

Vulnerability           Overbid by

Against                  2 tricks
None or Both          3 tricks
For                        3-5 tricks

Responses

The most common response to a weak jump overcall is to pass. You know your partner has already overbid by a number of tricks based on the vulnerability. Having a good fit and some strength can make bidding worthwhile.

Any raise of partner's suit should be to obstruct the opponents bidding or to sacrifice

Naming a new suit is a natural bid and not forcing on your partner. This bid can also be used for lead direction.

A cue bid is a game or slam try and is forcing for one round on partner. If he has a minimal hand he rebids his suit at the lowest level. A better hand allows the opener the freedom to make any bid he chooses.