You should be more bold with your contrast.

IMHO, More contrast (like double what it is and then a 1/3 more, don't be shy ;), is needed if you stick with these colors (which I don't like), however.... if you are trying for an "alien" the skin shades could/should be another color, dull, greyed, scaly, metallic....somthin. Secondary lighting always helps alien things, so try some of that. The overall proportions are also very humanoid, something "odd" will help get an alien feel (no neck is not enough). This is especially needed since you are only showing a part of the being. You have added a wierd space between chest and arms, REMOVE! When you update this let us know what the purpose is, avatar, game sprite, gift for girlfriend/boyfriend, learning....