1. If you open the map image in a paint program, then you can draw on it. Level 2 may allow you to concentrate better. Then after you've solved it, see if you can get past the monsters and robots...
2. There are no extra keys to waste, and Keen can only possess one key at a time for each color. Logical statements about sequence will help you solve the puzzle (i.e. "this before that").
3. There are only three red keys in the level. There is one red door in the beginning, and two red doors in front of the exit. What does this say about the other red doors? What does this say about the stone blocks?
4. Count the number of blue keys. The one in the beginning must be used on the first blue door. Count the total number of blue doors guarding the exit and red keys. Keep in mind Tip #3. What does this say about the other blue doors?
5. Count the number of available yellow keys, keeping in mind Tip #3 and Tip #4. Count the number of yellow doors blocking the exit and blocking the red key above the exit. What does this say about the other yellow doors?
6. Look for invisible bricks (dots in the upper left corners). There are two.
7. Now that you have eliminated several doors, you need to choose a sequence for opening the remaining ones. The green keys and doors will help you get started...
8. Don't grab every key you come across. Save some for later!