Optional selection is critical as it differentiates candidates when GS scores are similar. Don'ts: Don't follow trends, small syllabus attraction, popular teacher guarantees, or rumors. Checklist: Subject should be interesting/tolerable, sustainable for 3-4 years, have adequate study material and good mentors, consider competition level. Selection process: Eliminate unsuitable options, check remaining syllabi, research thoroughly, consider graduation subject, prefer subjects covering GS portions, test subject appeal through basic reading.