New to Pixel Art

I'm really new to pixel art. I'll post some of my examples for you to see. Do you have any tips/critiques for me? It would really help, as I desire to improve but lack the outside input of other pixel artists to help me. I essentially made all these up, I did not use any bases or things (not sure what they are called). I may try using bases in the future, but I have not decided yet. Also, I tried to resize the images so that you can see them better, so I hope that's okay! Thank you very much!

The weapons look cool.
But the human-furry thing is kinda looking mean. Maybe try doing something else with the eyes. Otherwise it does look good. I don´t do sprites in this format. I think no one does but i´m sure somebody could help you better then I do.

Are there different formats I should use? I'm sorry I just really don't know what I'm doing, but thanks a bunch for the criticism! I'll try something different with eyes in the future to make them look less...evil.

I agree with Yria, I think that the eyebrows make it look mean. Other than that these look good.

Good job and like Spartan and Yria, your wharacter seems to be a bad girl.