Instructions
Take the instruction course. If you're not familiar with DDR, it's wise to start out by learning how to step. You'll get a better sense of how to progress through the levels of difficulty. Completing a song on beginner mode will be accompanied by a short instruction of how to step so that you can improve.
Familiarize yourself with the songs. DDR Hottest Party has 50 total songs, and some must be unlocked. To maximize your score you will have to practice often and become familiar with the songs. Focus on the tempo of the song and coordinating your foot movements with the corresponding arrows as they move over the meter.
Maximize your score. Like the older versions of DDR, "Hottest Party" bases its point system on your step score and combo. "Marvelous, perfect, great, good, almost" and "boo" are for single arrow steps while "OK" and "NG" are for freeze arrows. Only maintaining a "marvelous, perfect, great" or "OK" for freeze arrows will count towards your combo tally. Your maximum score will be determined by your difficulty mode-beginner, basic, difficult and expert. Expert mode will yield the highest score as it generally has more BPM (beats per minute).
Strive for perfection. In order to get AA on DDR Hottest Party you will have to be nearly perfect. Your combos on the songs you choose must be maxed out. Most songs will not yield an AA score without the majority of your steps being "marvelous" or "perfect" and with all "OK" scores on freeze arrows.