My 1st UDK Map - I call it LakeView.
Here's a couple of videos.
Things I learnt :
1. Always, always block out the level first instead of going into details
2. Plan ahead if you are making multi-floor approach (like 2 floors or more)
3. Terrains are one-way objects.. means to say from below they are invisible
4. Design levels based on type of game. For something like Unreal Tournament don't waste time beautifying the level - players don't get a chance to enjoy them much, so focus more on elements that add up the fun.
5. If possible make copies of UDK assets in your custom package (don't edit the original)
6. Add bots and test out the level in the initial phase itself. You see, you can have this glorious imagination of bots acting like smartasses and doing cool things - but they don't.
7. Check out UDK documentation for path nodes and stuff. You can see the navigation map in the editor that shows connections and also color-codes the links. It's really helpful when bots don't use way points.
8. If you make a 3D editor - for fuck's sake don't use mouse right click for navigation.
9. Fog - very useful to blur out those distant objects. Use exponential height fog when possible
10. Never make a "forest" type of level for your first map. Foliages (grass, leaves, herbs etc) are hard to place - they can cause a hit on frame-rates. Experience will teach where to use and how much to use.
11. I use blender - use your scale properly. If the model is too small then even if you scale in editor, the lightmaps will still have issues. Also, if fbx is ASCII format - you can set default scale using notepad++ :P
12. These 3D level editors - any of them - be it UDK, Unity or CrySDK, they keep crashing. Always take backups of your files - multiple ones. Use them as check points. (For me, UDK removed a lot of foliages by itself and by the time I realized they were wrong I had made too many changes to just revert to old version)
NTFS: Recording game play, compressing and uploading videos is a fucking pain in the ass