This is a great question. Generally, looking for internships for your 3rd and 4th year is a good time frame but there are a few other considerations to take in.
If you are trying to either figure out what career you're interested in or which specialization you want within a field, it is very useful to look for shadowing opportunities as early as possible (even 1st year). Shadowing allows you to tag along with a professional in the given role to see what day-to-day activities are like and to ask questions about how they chose their career, progressed within it and any other advice they may have. It's also an excellent networking opportunity and a way to help determine which company would be best to pursue an internship with.
You can also explore volunteer options as a way to get some hands-on experience. This can also be added to your resume. I used volunteering as a way to help me explore different fields - from tax accounting, to community development, to business projects.
Finally, be sure to compare unpaid and paid internships for the best fit. An internship can get in the door of a company for more permanent opportunities or help build your experience base. They take more time and energy than shadowing, so look to get one after you've narrowed down the choices for what interests you. If you know in your 1st year exactly what you want to be, then you can get an internship then. But if you are still exploring, use shadowing and volunteering to help narrow down your choices. Try to start an internship by your 3rd year.
Ashley recommends the following next steps:
As early as possible. Many people have been able to start developing internship experiences during high school. The first thing that one needs to do is to develop an appropriate career focus and use internships, coop programs, volunteering, part time jobs, and other career exposure related opportunities to see the inside view of a job and get to know what people do, how they got there, and what advice and suggestions that they might have.
Getting to know yourself and how your personality traits relate to people involved in various career opportunities is very important in your decision making process. During my many years in Human Resources and College Recruiting, I ran across too many students who had skipped this very important step and ended up in a job situation which for which they were not well suited. Selecting a career area is like buying a pair of shoes. First you have to be properly fitted for the correct size, and then you need to try on and walk in the various shoe options to determine which is fits the best and is most comfortable for you to wear. Following are some important steps which I developed during my career which have been helpful to many .
Ken recommends the following next steps:
In my opinion, it is never too early to start applying/looking for internship opportunities. Your college career center may have parameters (juniors and seniors only?), but that should not prohibit you from inquiring at an earlier stage on your own.
Your career will be with you for the rest of your life. If you plan on having it be enjoyable and fruitful, there is no reason to put off what you can do today.
Suggest to do an honest assessment of what's the internship offering you and what is it that you Ave to offer for the hiring manager. It's got to be a win win for all, you don't have time to do too many and bad internships (that bring you nothing) before you go full time.