You could use the search function of the forum and will get tons of info on that.
It's been asked a lot.
EC: Clubs, sports team, volunteering (medical and/or non-medical), student body (president, senator etc.). Your school will have a website for this, most likely. Hospital volunteering, ask the hospital volunteer dept.
Shadowing: you could try cold calling if you can find a phone number or e-mail of a physician, but usually being referred by your primary care physician or pre-med advisor is easier.
Research: ask your professor, or look for paid internships available for the summer across the country. The ones offered by schools usually have a deadline around Feb ~ April for the following summer. Company internships will vary. Search "uc davis summer paid internships", they have a nice PDF file of internships offered in US schools and prestigious medical associations etc.