Naji
The best tip i can give a beginner is to keep it simple. Have a look at flat design things for example. They are really up to date at the moment and with a little understanding you can make really beautiful things.
Have a Look at Dots-Game -> http://www.wittysparks.com/wp-content/u ... iPhone.jpg
It´s based on super simple shapes but it´s looking absolutely polished. Drawing different things like chicken or humans or whatever can be pretty hard in the beginning, try to scale details down to a level that it looks charming.
Also try to get a better feel for colors. Looking at your stuff, it looks kind of "base-palette-styled". Don´t use to saturated ones, try to keep it in the same mood.
Adobe Kuler offers a very handy tool to find some color-system to go with on your game design. You will see that these colors really fit together....
http://wscont1.apps.microsoft.com/winst ... 000003.jpg
Hope it helps. <img src="{SMILIES_PATH}/icon_e_smile.gif" alt=":)" title="Smile">
Greets from Beaverland!