The two young women are somewhat similar, although Hermia seems to be more determined and more of a leader and Helena more of a follower. Hermia is the slightly prettier of the two and Helena the taller. Hermia seems slightly more assertive and Helena more diffident.
The two young men, Lysander and Demetrius, also appear relatively similar, although Demetrius appears the more self-serving and fickle. He appears to behave rather cruelly to Helena and opportunistically to Hermia, and he regards love somewhat transactionally. Lysander is the more romantic of the two, genuinely besotted with Hermia.
Oberon and Titania are king and queen of the fairies. Both are magical creatures of great power, accustomed to getting their own ways. Puck is also a magical creature, mischievous and generally benevolent.
The mechanicals are comic foils, naive but serious about doing a good job with their play. Bottom is bombastic and egotistical.
Theseus is portrayed as a good leader, wise, gracious, and generous, issuing sound judgments and suggestions.
One thing we know about Hermia is that she is very bold and self-assertive. We even see her boldness and assertiveness in the very first scene. When her father Egeus petitions Duke Theseus to punish Hermia with the full force of the law should she continue to refuse to marry Demetrius, Hermia very boldly states her own position. For example, immediately after hearing her father's side of the story, Theseus argues in his favor by saying to Hermia that "Demetrius is a worthy gentleman" to which Hermia very boldly replies, "So is Lysander" (I.i.53-54). Hermia even apologizes for her boldness in the next few lines, showing us that two of Hermia's personality traits are certainly boldness and self-assertiveness.
Helena, in contrast, suffers from insecurity due to Demetrius's rejection of her. More than just rejecting her, they were actually engaged before he started pursuing Hermia. As a result of her insecurity, like most women who become insecure due to love tribulations, one of her personality traits is being diffident, meaning "lacking confidence in one's own ability [or] worth" (Random House Dictionary). We first see evidence of her diffidence when Hermia greets her with the exclamation "fair Helena" and her only reply is to mope about how Demetrius thinks Hermia is fair and not Helena. We further see evidence of her diffidence when she decides to throw her friendship with Hermia to the wind and tell Demetrius of Hermia and Lysander's plan to elope and run off into the woods with nothing more than the hope of receiving a thank you from Demetrius for the news. Since this act of betraying Hermia really will gain her nothing, it shows us her underlying feelings of lack of self-worth.