Positive:
* Adept: Skilled and proficient.
* Amazing: Inspiring wonder and admiration.
* Amicable: Friendly and harmonious.
* Astounding: Extremely surprising or impressive.
* Attractive: Pleasing to the eye or senses.
* Admirable: Worthy of respect and approval.
* Affectionate: Showing love and care.
* Agile: Able to move quickly and easily.
* Alive: Full of life and energy.
* Ambitious: Having a strong desire for success.
* Angelic: Like an angel; pure and innocent.
* Artistic: Creative and skilled in the arts.
* Audacious: Bold and daring.
* Auspicious: Promising success.
Negative:
* Acrid: Sharp and bitter.
* Afraid: Feeling fear or anxiety.
* Aggravating: Making something worse.
* Aggressive: Hostile and forceful.
* Aloof: Unfriendly and distant.
* Angry: Feeling or showing strong displeasure.
* Anxious: Feeling worried or nervous.
* Awkward: Clumsy and uncomfortable.
* Apathetic: Showing or feeling no interest.
* Arrogant: Excessively proud of oneself.
* Artificial: Not real or natural.
* Ashamed: Feeling embarrassed or guilty.
* Awful: Extremely unpleasant.
Neutral:
* Active: Energetic and engaged.
* Ajar: Slightly open.
* Ancient: Very old.
* Apparent: Clearly visible or understood.
* Atypical: Not typical or usual.
* Aware: Conscious of something.
* Absent: Not present.
* Accurate: Precise and correct.
* Adept: Skilled and proficient.
* Alight: Lit up or illuminated.
This is just a small sample. There are many more describing words starting with "A". The best word to use will depend on the specific context.