You probably all know about the Great Designer Search 3 happening as we speak, if not you should really check it out here:
1) JUDGING THE DESIGN TESTS
2) DESIGN CHALLENGE 1: YOU MIGHT AS WELL TRIBAL
3) DESIGN CHALLENGE 2 : A CIRCUS ACT
3) DESIGN CHALLENGE 3 : FINDING A GOOD MECHANIC
This is not really a contest because I don't think there are enough people on MTGCardmsith that would take it (the GDS3 challenges are really time-intensive with something like 10-ish cards to design per challenge.) Nonetheless, if any of you have done them at home (or wants to do them now) and are interested in some constructive feedback, I'd be happy to look at your submissions =D
P.S: Some additional thoughts:
1) All the rules are at the beginning of each article above.
2) Try to submit your designs the same way it's templated in the GDS3:Name (rarity)
Card Type – Subtype
Power/Toughness [IF CREATURE; SKIP OTHERWISE]
3) For the first design challenge (You might as well tribal), try to avoid creature types that were already done by the contestants: Horror, Insect, Ooze, Shaman, Rogue, Aetherborn, Imp, Samurai.