I like to do abs first when I feel the best and can have the most intensity. Stick to a few exercises, the ones you can feel the most. Alter resistance and weight for different exercises in the day, and switch which ones are "heavy weight" and "light weight" throughout the weeks. Usually I do hanging leg raises, hanging pike, decline bench situps, cable crunches, and hanging windshield wipers. I also substitute in some ground work such as cross-body crunches, bicycle crunches, toe-touches, leg raises, etc. As for arms, like the guy above me said, work bis and tris in one day, and maybe do some forearm/ grip work at the end. Try supersetting a bi exercise with a tri exercise, and perform drop sets,* warm-up sets*, vary weight, and try a pre-exhaust set of extremely light weight and 100 reps. Keep at it and good luck!