Happy people don't need to put others down, to bring themselves up.
Happy people enjoy taking the time to make others feel happy and good about themselves. This is probably the biggest one. You can't cheer someone else up if you're not happy yourself. It also goes the other way, when you're cheering someone else up, you automatically are filled with happiness yourself.
Happy people don't tend to take life too seriously. Happy people are "light" on the inside, and that carries through to their external body - it shows. They radiate a warmth and loving energy that quite literally affects everyone around them.
Happy people are often naturally giving by nature, selfless, and compassionate. This stems naturally from a place of love - due to the fact that when one is at peace with themselves, there is nothing but light energy, an openness, and love. Love/light cannot thrive in darkness, or negative energy. It's impossible.
Then there are those that are unhappy. Obviously when one is unhappy there is no peace within. There are issues that haven't been dealt with, and ego is almost always involved. Unhappy people radiate a darker energy. Have you ever walked into a room with an unhappy person? You can feel it with all of your being. You can feel the negative energy without anyone saying anything at all.
Unhappy people are always unhappy with themselves first. You cannot be happy with yourself, and negative towards other people. Again, light vs darkness. Not possible.
Unhappy people are often fixated on little things that are turned into big things. It takes on a snowball effect where they dwell on things until they can no longer bear to be around themselves, and are forced to make a change or fix the situation.
Unhappy people are often selfish (ie: too focused on themselves in that moment to be able to have compassion and sensitivity for another, or better yet, even compassion for themselves), so in summary they are blinded by Ego. Ego is mind-identification. Identify yourself by your mind and you're asking for trouble. It's a facade. It's covering up your natural state of being which is happiness; light; love.
There is a wonderful quote by the Dalai Lama - "If you want others to be happy, practice compassion. If you want to be happy, practice compassion."
A HAPPY person is compassionate with themselves & others, and forgiving of themselves and others. This automatically leads to happiness and joy.