While it is important to keep an open mind (esp during 3rd year) since you may change your mind about what you want to do later - ortho is extremely competitive and as previous posters have pointed out there are some things you can do to make yourself a potential player come this time during 4th year.
You need to get a killer Step 1 score. This is single-handedly the most important thing that will come out of your first two years of medical school unless you have some ridiculously significant research under your belt (but you've already said that wasn't for you). The best way to do this - as cliché as it sounds - is to learn the material well during the first two years. You'll kill two birds with one stone by getting good grades hopefully during the pre-clinical years as well (which may be important for AOA). Most of the rest of the "important stuff" comes in the clinical years. Third year grades are extremely important and I'm not just talking about your surgery clerkship and your ortho elective. I was asked by an ortho PD "Well what did you get in your internal medicine rotation?" Who cares about IM if I wanna do ortho? --> THEY MIGHT, because doing well in other speccialties shows that you're probably a well-rounded medical student and that you can excel in fields that you're not necessarily interested in. Then during third year or usually fourth year you probably wanna do a home sub-I and a couple away rotations. Its a little early to start thinking about this, but as far as the home sub-i goes... As someone pointed out earlier the more ppl you know in the department the easier it will be to get good, personal LORs when it comes time to ask for them and these are important! Get to know people early - residents, attendings, the PD/chair. Go to the ortho interest group meetings (or start one if there isn't one maybe). This is clearly not an all-inclusive "must do" list, so you need to gauge where you'll get the biggest bang for your buck in terms of what you focus your time on. The following documents can help because they show you what the "average" applicant looks like (for all fields, not just ortho), and also what the program directors look at as being the most important part of your application (again for all fields).
http://www.nrmp.org/data/chartingoutcomes2009v3.pdf
http://www.nrmp.org/data/programresultsbyspecialty2010v3.pdf