https://www.reddit.com/r/selfimprovement/comments/7w3it5/any_good_subreddits_related_to_self_improvement/

• hair
• skin
• clothes
• facial expressions
• appropriate amount of eye contact
• body language and posture (way more important that most people think)
• fitness / body shape in general
• smell
• "swagger", how you compose yourself and stride
• conversation
• appropriate amount of attention and interest displayed in tone
• very important is not placing them with too high or low worth in your life. Too clingy or distant is probably the biggest reason sparks die.
• not too slow fast pitched voice
• charisma and how eloquent you are
• conversation topics
• how blunt / subtle you are
• how you react in general, the emotions you seem to process
• if you can't notice an area you need to focus on without it being pointed out then most the time you're fine. Definitely about a million more I could have named but those are the ones that jump out.