When you first start your concept or sketch just have fun, enjoy sculpting and don't over think things. Try to just relax and let your subconscious take over, doing this may release some ideas you didn't even know you had. Good and bad ideas are good to come out, the good ones can turn into masterpieces and once the bad ideas are out you wont have them holding your imagination back. Once you come up with a piece that you are happy with and enjoyed creating it is now your job to really bring it to life. The best design out there is still plain and boring without emotion, a great expression and sense of character can bring interest to a plain design so when you combine your cool new idea with a sense of character that can connect with the viewer it will take it over the top. Try to move your character around, feel what he feels, and think how he thinks to truly understand his being. Now you will have the best chance at bringing the inner sense out and connecting on a deeper level with you and everyone who views the piece.
Here is a new piece i am working on.
First up is my concept, i did a warm-up sketch starting from nothing and not knowing what i was going to do
Then i liked the concept so i continued to work on him and his body language. This character is suppose to be the first invader or visitor, i wanted him to be a larger creature looking down with a stronger menacing look. Then for the base i continued with this idea and created a stony style base with ancient writings, all of them made up but with reference and similarities to Chinese, cuneiform, symbols and even an are with crop circle geometric symbols.
Make sure your character makes sense and gives you a certain feeling when you look at them. If you don't get excited and anxious then something is wrong. Figure out what it is and fix it, or let it die and start fresh.