The specific qualities that fraternities want vary from group to group. Some frats look to find new members who have similar personalities to the existing membership. Others strategically look to complement existing members with pledges that bring something new to the table. While you don't want to play a part to try to fit in, don't be afraid to showcase your personality when you arrive on campus. Being friendly, funny, helpful or assertive in classes may get you noticed for recruitment. During the pledge process, your personal qualities may simply mesh well with what the group wants.
You can set yourself up for success by researching fraternities early on. The campus Greek life adviser or director of student life can often give you great insights into the makeup of various groups. Some emphasize social activities, while others also get involved in community service or focus on program-specific activities. Identifying the frats best aligned with your goals and personality puts you in a better position to approach leaders in that group. A Greek adviser may even make the introductions so you can get to know current members.
Above all else, current members want to recruit and accept pledges who will make a strong commitment to their brothers and the organization. In essence, your informal getting-to-know-you conversations and formal efforts during rush is your screening process. Diving in and taking the time to make connections with a number of brothers puts you in the best position. If a frat is right for you, you shouldn't have to press too much. You should find natural connections.
While you can do a number of things to improve your ability to get recruited or picked for a frat, the ultimate decision is out of your hands. In some cases, fraternity members strategically plan to fill open slots with certain types of people to address voids or to strengthen the overall group. Being turned down isn't necessarily a personal affront. You may just not fit the mold of what the brothers were looking for.