Here are some tips from the forum or from me...
1. NEVER use segments or entities over and over again try to use new media each level
2. While making a game keep the levels with many path ways to make it more realistic... it keeps the plr wanting to play the game
3. When making landscape try to make it look natural because mountains dont repeat in shape and size do they?
4. Dont post boring screens try to make it look like you are serious about making a game
5. Lighting does help but sometimes there are moments where you may not need it
6. When using lighting try to make light sources
7. Try make a level progressing through the story try to make each level different
8. do not make many large areas... it is harder to fill up areas with entities like this
9. never make a level only a hallway thats continues forever thry to add rooms that you need to enter
10. add some obstacles to jump or crawl over/ under it wil add some thrills to the game
11. try to give the player a good description of what to do in the levels... it would help players know what to do and also tie into the story
Well that all i know for now hope this helped!!