The most important suggestion is to actually work in an industrial environment. Doing so provides experience in what goes on in an industrial job as well as an opportunity to determine one's aptitude for, and interest in, industrial employment. In addition, the best reference when applying for a job is solid evidence that one has already accomplished something similar. The government is probably the best source, since there are fewer institutions to contact and there are often specific programs to support summer employment. The government also has employment offices which have lists of available positions and directions on how to apply.
Large companies have personnel offices which can provide the same kind of information.
These methods can be successful, but they require work. An even better method is to get a contact inside the company. One approach to this is called networking. Talk to your friends, acquaintances, professors, etc. Let it be known that you are looking for summer employment.