I'm assuming you're at a university that has labs with grad students / post docs. If you don't have a direct "in" to any research positions, the best thing to do would be to follow these steps, in order:
- Read up on what professors at your school are working on, figure out what you're interested in, etc. You don't need to know their work inside and out, but you should have an idea.
- After you've narrowed your choices down to 2-4 labs, show up at the labs and find a grad student or post-doc, state your interests, and ask nicely if they'd be able to talk to you about potentially working in the lab and what the PI's policies are. If the first person you talk to isn't helpful, look for someone else. They may just be in the middle of an experiment and don't have time to chat.
- After getting some info from step 2, send an email to the PI, mention who you've talked to and what you're interested in, and ask if they'd consider meeting with you to discuss possible research opportunities.
If you follow those steps, don't piss off people (i.e., be polite, respectful, and understanding if someone doesn't have time to talk to you the immediate moment you show up), and there's room, you'll almost certainly get a position in one of your top choice labs so long as your grades aren't terrible.
Cold emailing professors doesn't work.