If you are a junior in college make every effort to get a summer job in a field that is in any way associated with your major or better yet with a company in the field that you think you might like to work in. This will give you "real world" experience, no matter what the job actually is and you may find out that you really like or hate the company/field. Very valuable information. Many companies will look at "summer employees" for permanent jobs first. I have heard of job offers being made before the end of the summer job.
Once you are a senior, you really need to figure out where you would like to work, what field you would like to work in and lastly, which companies you think you might like to work for. By the end of your first semester, you should have a resume completed and a list of companies that you think you might like to work for compiled. At the beginning of the your last semester, tailor your resume for the specific company and job that you would like to interview for and then send it out. Do this for each company on your list. A focused approach tailored for each opportunity will give you the best chance of getting an interview. Focus on what the job posting is asking for and then via. the resume and brief cover letter, explain why they should give you an interview . These resumes and letters should all be sent by the middle of your senior year. Earlier is better than later. The objective is to have a job offer (hopefully more than one) before you graduate.
Sending out a mass distribution of your generic resume at graduation time is not very effective and does not set you apart from the hundreds of other resumes the company will be receiving.