Some thoughts on trying to find a rare bird, from someone who has spent an unreasonable amount of time doing just that...
- Chance favours the prepared. ID knowledge of both common and unexpected bird species is an asset. An awareness of potential vagrant occurrence also improves your chances. When vagrant hunting you should also expect to find aberrant plumages of common birds, rare subspecies, unseasonal plumages, early or late migrants, escaped exotics, etc. Photograph birds for future study and learning.
- Consider a "detectability bias" when learning about patterns of vagrancy. Cryptic rarities are likely under-detected. (e.g., hard-to-identify birds like gulls, or hard-to-locate birds like longspurs). More flashy birds may be harder to "find" (e.g., Varied Thrush records are likely high due to their bright colouration and frequent appearance at bird feeders where they get noticed and photographed).
- Birding at concentration points will give a greater return on your effort. Visiting locations with a diversity of habitats can further improve your chances. Finding ways to get better looks at birds (i.e., closer and longer views, ideal light, shelter from wind and rain) increases your chances of spotting AND identifying an unusual bird.
- Be prepared for slow days. By nature, rare birds may be going against the grain, so your best odds of finding vagrants may bring you to locations with low activity for the current season. Also consider checking areas with low observer coverage.
- Expand your search radius in the field. Use lower powered optics (e.g., 8x binoculars vs. 10x) for a wider scan. Don't just focus on one area (e.g., the horizon) when birds may be up high or right on shore. Also, try not to skip many birds as a vagrant may be on the fringe of a flock.
- Keep an open mind. Learn about difficult identifications from the perspective of "why not" as well as "why". (Just don't report your "why not a ..." to the local bird listers or they may get upset with your active learning process).
- The more frequently you go birding and the longer you spend in the field (looking, not driving!) is the best* way to improve your chances of finding rare birds. Incorporate an understanding of how weather affects bird migration and vagrancy to enhance many of the above points.
- Have fun!
============================================================= *actually second best... having fun is the most important part...