It's a shame you decided to use an alt, because I could look at a few of your posts and tell you exactly how you could make your posts longer. But here's some general "tips and shit"

-Write in more detail. Write exactly what the character is doing instead of a one word summary of the action. Don't just "mix a potion," explain how the potion is being made. Where did the herbs come from? what do they smell like? Did you need to boil any water for this? Is making potions a mundane skill or is it actually really hard? 

-Write what your character is thinking. You have to be careful with this one. Some people have a tendency to write every mundane thought they have, but it's certainly welcome to see how a character makes a choice or a decision that doesn't normally side with the way they operate. 

-Write the history of something, or a character's history of something. If your character finds themselves in familiar territory, write a brief description of why they know this place or how they know how a particular device works.

-Educate your readers. I'm constantly reading articles about things my characters are into so that I can better explain what they are doing or why things work a certain way. Your average reader probably doesn't know how a mountain climber ties off their equipment, that an alligator has a transparent third eyelid for hunting underwater, or that a blow fish's liver is the most poisonous organ in its body.

And as [@Ammokkx] already pointed out, there needs to be a reason for it. Nobody wants to read an empty post that was long for the sake of being long.