The Sun sign is a character's inner nature, the Moon the emotional nature and the Ascendant the face shown to the world. Seldom does one character be a pure sign most of the times they have two of three signs in their nature. Bear this in mind when you're creating your characters and layering them. But let's begin
For a character with an Aries Sun think action. I always have a picture of someone sword in hand leading the charge. Aries can be aggressive and direct in expressing themselves. Creative energy abounds but they can invest everything they have into a new project until they lose interest. They need to prove themselves through action and are often impulsive, acting first and then thinking. They may ignore the advice of others. Often they don't finish what they start but they are competitive. Recognition is their need. Their strength is in their refusal to accept defeat.
Now the Aries Moon which expresses emotions. Here the emotions can be volatile, impulsive. They may not consider the consequences of their actions. While their temper might flare, the anger is temporary and easily forgotten.
The Aries Ascendant is the face shown to the world. This character will project intense energy and decisiveness. They will act on their ideas immediately and hate wasting time. They are competitive and have a desire to excel and to prove themselves through action.