1) Work Product
2) Hours put in
3) 2L Grades
4) Attending social events
5) Being well liked
6) Working in an active practice group (i.e., lit as opposed to corp)
7) Working in a single practice group rather than moving around
I have a family member who is a hiring partner. I've been told the following:
1. Work product. Great work product can trump most things. In the end, it's your work product that they are selling. Said hiring partner has given offers to people who were generally disliked and even made somewhat of an arse of themselves during firm events because their work product was excellent.
2. Being generally liked/desired. This collapses several of your points. If a practice group head tells the hiring partner "I want X", then X is going to get an offer barring some other extraordinary circumstances. There are of course, a variety of reasons why a partner would think that of a SA. It tends to be a mix of work product and personality. It also may depend on pre-law school experience that jives with the practice group.
Other factors fall into the "can only hurt you" category.
1. 2L grades won't matter unless they fall to the point of being worrisome. If you had a 3.7 1L year and a 2.7 2L year, that could cause problems. Falling from a 3.7 to a 3.6 is no big deal. By contrast, going from a 3.5 to a 3.7 probably won't really help you.
2. Practice group can cause a no-offer if you make them think that you are dead set on a practice group where they won't be needing anybody. Telling them, "All I've ever wanted to do is securitization work" could be problematic.
3. Don't anger anyone. Sounds easy enough, but you would be surprised. Make sure you know what expectations are RE: deadlines. If you tell someone you are going to do something, do it. Generally, don't be flaky. One of the main things that can sink a SA is someone from the firm complaining about them (even if it's kind of petty).
4. Being a complete social outcast can be a problem too. You don't need to be the life of the party, but if you spend all if your time staring at your shoes, people may speak ill of you.
5. General unprofessionalism. At said hiring partner's firm, there was once a summer who would walk around the office without shoes on (just socks). That kind of thing can also get you dinged.