1. Before making a terrain, always think you're making a world living inside your imagination.
2. It is good to plan ahead what will be inside this world (plants, doodads, trees).
3. Do not try to put every element of warcraft III objects to this world.
4. Make a specific theme (always works best).
5. Do not use the random height field, it is a noob feature.
6. Always pick a the water cliff level, then increase the height field of the map using huge brush to coverup the water.
7. Learn to love you're mouse before you terrain, it is your drawing tool.
8. Plan ahead whether you're going to do a realistic approach and unrealistic approach of the terrain.
9. If realistic approach, search for custom tree models and custom grass models.
10. Also alter the scalings of each doodads, trees, structures, and other stuff.
11. Do not use cliff's if you're doing a realistic approach.
12. If unrealistic approach, open up few melee maps and learn how the terrain works.
13. Do not just put random trees and rocks and stuff, always think of a pattern in the terrain.
14. search for pictures of your landscape on google.com
15 .Thou shalt not use blizzard trees.
16. Thou shalt know that fog and atmosphere play a large role in your end result.
17. Thou shalt not use blizzard cliffs.
18. Make an outline of your terrain in the editor using tiles
19. Practice using blizzard doodads and units to sharpen your creativity with a limited palette.
20. Do not rely on custom models. Many amazing effects can be done with what you're already given
21. If doing a natural landscape, find out how plants and natural elements work in real life.
22. Be sure to check ability and buff models. They have a large variety of useful items you can add to your terrain.
23. Learn to use units tastefully. Nothing like overcrowding a terrain with units to depreciate its value.
24. The angle you take your screenshot from plays a big role in how your terrain looks.
25. Dont be afraid to get inspiration from other's terrains. Just dont copy them.
26. If it looks good, it IS good. Same in reverse, if it looks bad, it is bad.
27. Do not be scared to use ctrl, Page up/down.
28. Don't be scared of what other people think, they might help you.
29. Say NO to Noise! (Even though I used noise a bit in my map.. becuase I'm not very good at terraining!)
30. Don't use big brushes, use small brushes when terraining to give details.
31. To make a mountain, increase the height field of a particular area and change the terrain to rocky terrain.
32. To make a good fog, sometimes the combination is y = 1000 z = 6000 density = 0.6
33. You can actually modify the sky display, just open up mpq editor look for the sky skin file and change it to your preference.
34. Always match the color of the fog with the sky.
35. Kevin Costner is a bad terrainer.
36. Turn Antialiasing (AA) to as high as possiable before taking a screenshot (smoother looking terane and objects).
37. Turn Anisotopic Filtering (AF) to as high as possiable before taking a screenshot (to make the terane and object textures far away look better).
38. Do not digitly enhance your terane using an art program.
39. Think before pressing "Print Screen".
40. Do not show blank map edges or unfinished areas in your pictures.41. Use tile variation! Make sure that you do not use too much nor too less.
42. Read terrain tutorials from the tutorial section, they will help you a lot if they are good.
43. Crop your pictures before posting them!!
44. Try to be creative as much as possible, but do not make it too unrealistic
45. Do not create pointy bumps with a 1 size brush, use a bigger brush to make it smooth.
46. When using plateau, always remember to smooth out the edges
47. Use different tiles from other areas, but make sure that they go well with the rest of the terrain.
48. Do not think taking a Computer Science class solves everything for making games (maps), learn how to do the art!
49. Try to advance your terrain to become part of a dynamic world.
50. If your making TD's, Castle Defense, Hero Arena, or Maze, do not substitute the gameplay balancing with the terraining.
51. While terraining try to turn on the Grids, works well if you want to balance your terrain, determine the height field comparisons.
52. Do not dream of making a good citiscape or dalaran terrain without 200% custom doodad enhancement.
53. It is sometimes best to work randomly while terraining which gives a naturistic sense of art to the end-product.
54. Replace cliffs with pathing and sight blockers.
55. The key "p" is used to show the pathing in the terrain.
56. Read here for Castle Terraining tutorial.
57. Read here for Making rivers and lakes.
58. Make melee buildings become doodads and transform an area into a real city!
59. Do not use wc3 original trees, they look like sticks.
60. Chuck Noris is a bad actor.
61.Don't have absolutely 100% custom doodads unless there is nothing included in blizzard models that you need.
62.Make sure that your terrain(if its natural) Looks REALISTIC.
63.Don't be afraid to use Buildings as doodads, its completely fine.
64.Don't touch 'raise cliff' or the blizzard trees unless really necessary.
65. Oversized bushs make good trees
66. The Object editor is your best friend
67. NEVER, EVER EVER EVER EVER NEVER FOREVER
68. NEVER EVER FOREVER EVER, Use a square brush for making water.
69. Be Creative!
70. Dont overcrowd your terrain with numerous doodads
71. Tall and short doodads look better when placed near eachother rather than near other tall/short doodads
72. UTM owns you
73. UTM owns me.
74. Don't use blizzard cliffs!
...
101. Reread this guide.
More to be added, possibly. 
