Lydia's choice in husband, the fickle, shallow and irrascible Wickham, reveals her own shallow, fickle and flighty character. Wickham isn't that great of a guy; in fact, he is quite a scounderel in many ways, but Lydia is fascinated with looks, charm, and her own spontaneous ways. So, she doesn't do her research on the guy, lets him sweep her off of her feet, and runs away without any thought of what it might do to her reputation or family. She never really cared what others thought of her or her family, and often did tactless things to embarrass them. Wickham was reflective of that nature. His own foolish habits (gambling, lying, etc.) led him to make another foolish choice in Lydia.
Jane's choice of Bingley reflects her sweet temperment, kind nature, and polite, submissive personality. He is the "appropriate" choice; he has a good income, is handsome and charming, and very polite and proper. This mirrors her own nature. Jane is not a rebellious type, so would marry a good match to please her family and situation, but she is also very kind and nice, as Bingley is. Bingley is a sweet, sometimes naive guy who could never do anyone harm, and he complements Jane well in those areas. Her proper courtship, her silent longing and suffering when he leaves, and her joy at his return and proposal are all very Jane--she is the silent, kind supporter who deserves such happiness.
Elizabeth's choice in Darcy reveals how she doesn't care as much about social conventions, or appearances. She does at first, thinking him to be a snob, but once she gets over that, she realizes his true nature and that it doesn't matter that he comes off as aloof to others, because deep down he is an amazing person. Darcy is a true friend, kind, loyal, and generous. He is also proper, modest and does things not for praise or attention, but because they are right. At the same time, he doesn't go out of his way to appear pleasant or to fulfill social norms; he realizes those things don't matter as much as one's inner self. Elizabeth is, in many ways, the same. She rejects the "proper" choice of a husband in Collins, because she realizes the shallow nature of his character beneath the qualifying resume. She often does unconventional things, and doesn't fit the mold of the perfectly trained, educated, and groomed woman of the time, and she is fine with that. More important to her is character and true affection, so Darcy is a good match for her.
I hope that those thoughts helped; good luck!