If your an undergraduate, a lot of times you will be working under a graduate student, helping them in their graduate research project. A good way to get into a lab isnt always to get to know a professor which runs the lab, but get to know the graduate students that do the research. I and few other graduate students I worked with hated it when our PI dumped an undergrad on us to train and help in our project, especially when the undergrad has no clue about what the research is on. It can take a lot of the grad students time up and some times set back their progress...thats when the undergrad ends up doing nothing but washing dishes, as that is the easiest thing to train someone to do and it saves grad students a lot of time, but doesnt really teach undergrads anything and doesnt really make for any interesting stories for med school interviews.
Depending on how your school's graduate program works - a lot of schools masters and PhD students teach either laboratory courses or some lecture courses under a professor - if your school is like this, then I would suggest taking one of these courses and getting to know the graduate student. For instance, in graduate school I instructed Microbiology Lab for pre-meds/Pre-nursing students. Find out what his/her research is on, and if its interesting to you, ask them if you can do undergrad research under them (Of course, do well in their class too)...If they go to their PI and tell them they found an undergrad that wants to do research, you shouldnt have a problem getting into the lab and the graduate student will be more likely to trust you with their research. Trusting your undergrad is extremely important as a graduate researcher, largely due to the fact that your research is your degree, and you dont graduate until you finish that research... So, keep that in mind when you approach a graduate student about research. One easy way to gain the trust of the grad student, something that I have found rare in my experience, is to get copies of the literature behind the grad students research, and read it, understand it and question them about it....All in all GET INVOLVED.
In my opinion, to get on publications, simply doing research as an undergrad often wont be enough unless you get in on a project more or less from its beginnings, or you spend quite a long time in the lab on a single project to make a significant contribution to the work. On top of that, there are a lot of graduate students out there that are extremely stingy with their publications. For example, during my graduate research, I did 8 months of sequencing work, 8 hours a day, 4 days a week, to help another grad student get data she needed for a publication, and I didnt even get acknowledged on the paper. So, be cautious of the person you work for/with, make sure they arnt an a**.
If you are able to get ahold of the literature behind the research and understand it, try and come up with small side projects which coincide with the grad students work. This, in my opinion is the best way to end up on a paper with decent authorship, or if the grad student isnt an ass, possibly your own paper with the grad student as second author. I emphasize small with the project because it will be easy to convince the grad student / PI that you can undertake it on your own/under the grad student's guidance. And if its small, it wont require a lot of time from the grad student away from his/her main project. When I was in graduate school, one of my undergrads came up with an awesome side project to one of my side projects, and it actually developed into a masters project for her..and she's been getting ready to publish the work as a first author.
One last word of advice...Only do research if you are truly interested in research. I cant emphasize this enough. If you go to a graduate student and even a lab PI and tell them you just want to do research to look good for medical school, you will end up washing dishes. As a graduate student I went through around 6 undergrad researchers, all pre-meds, before I found one undergrad that was actually interested in the actual research..hence, she stuck around to do a masters degree. Its not hard to tell which ones the good ones are - good ones show up between classes to do anything that needs to be done (even wash dishes), read all the literature they can get their hands on, and arnt afraid to say they dont understand something.
Research is not like your science class labs, it can be a lot of work and a lot of times very boring and tedious when you have to tweak things over and over again to get them to work. But it can also be exciting and rewarding when you get the damn thing to work or when complex ideas all come together. If your not sure if your interested in research or not, be honest with the grad student/PI, and while you might still get a spot in the lab as a dish washer, you'll get your foot in the door and be able to see what research is like without interfering with the graduate students progress. What ever you do, dont waste the grad. student's time...Between their teaching, classes, bitch work for Post-Docs and PIs, and their own research projects, a lot of grad students have very little time for B.S..
Hope I didnt ramble too much and understand that this is from my experiences as a graduate and undergraduate researcher. Things may work differently at differnt universities..Feel free to PM me if you have some questions.
**Edit**- Sorry if I harp on "Dish Washers" a lot. I dont mean it as an insult to anyone who has joined a lab and ended up doing it. As a former graduate student, I really appreciated those students who were willing to come in and just wash dishes as it saved me a ton of time. And, most people dont realize how important washing dishes really is - especially in something like Microbiology, where any sort of residue left in a dish could result in contamination and ruin a project. So, thx to all those dish washers out there!