Here are some very successful sample abstracts from a range of different disciplines written by advanced undergraduate students.
Notice that while all of them are strong, interesting, and convincing, each one was written at a different point in the project’s process. Some (like Benjamin Herman’s history abstract and Diana Dewi and Jennifer Kittleson’s apparel and textile design abstract) include nearly final results, while others (like Laura Silberman’s curriculum & instruction abstract) include preliminary and projected results.
Notice also that even both across and within disciplines, abstracts differ in the amount of emphasis they give to objectives, methods, results, and conclusions. Depending on your particular project and your discipline, you will need to decide which of these aspects you will emphasize the most.