This list doesn't presume to be comprehensive. It's just a collection of observations and the mistakes I've made and seen others make while learning Lightwave.
1. Less is more - take a leaf out of the Bauhaus people's book and restrict the amount of polygons as much as you can. Someone new to 3D will be impressed with how many polys it took to create a scene. Someone more experienced will be impressed with how few polys it took. This applies especially to freezing metaform objects, where the default setting of 3 levels of subdivision is often unneccessary.
2. Change the light colours and angles. No light in nature is pure white. Make the lights yellowish, reddish, blueish or whatever to create a more naturalistic feel. Also, if you have your lights too close to the camera your objects will appear flat. Positioning the lights so that their light falls at an angle across the object means you will get more meaningful shadows. Finally, if you want flat and featureless (boring!) images, use a lot of ambient light, which washes out shadows.
3. Amass surfaces. Use that little button in the surfaces dialogue box called 'save surface' to build up a library of surfaces and add texture maps, bump maps, scans etc. . In this way you build up a library of images which are unique to your images, you can call them up quickly during a project, and you don't end up with a 'symphony in fractal noise' image, of which there are quite a few. There are some texture maps on this site, on the Texture Gallery page, and surfaces can be taken from the various meshes on the Mesh Gallery.
4. Structure your surface/object/image libraries with forethought. Sooner or later this will happen to you. You call up a scene file and suddenly get about 20 messages saying that such and such texture map cannot be found and you have to tell Lightwave which directory you moved it to since you last saved your scene file. When setting up a texture library, think about what images you will be likely to be creating in the future, and create folders for them. An example top level of directories might be Space, Nature, Metals, Reflection Maps, Transparents, Misc etc; and a sub level of Transparents could be Glass, Gems, Water etc.
5. Invest in reference materials. You don't get inspiration from staring at a blank computer screen. There's a mass of incredible images at your local bookshop, on the magazine racks, in your local library, in the papers, all from people who have spent a long time creating original images. Pay them the compliment of being inspired by their images and taking the idea forwards. In this way, we may see slightly less images copied from Star Trek.
6. You are the creator, not the software or hardware. So often you hear people banging on ad nauseum about how Lightwave is better than 3D Studio Max or vice versa, or that a Mac is better than a PC, or you need a superfast computer to do a particular task etc. I'm not sure what it is they are really saying. Are they saying 'I'm a better designer than you because I use this software' or 'If I don't use this software I am useless as a designer.'? The fact of the matter is yes, some packages do offer more features, a better renderer or a better modeller than others; but a good designer with a primitive system will always produce a better result than a bad designer with an advanced system. Work on your design skills.
7. Blend opposites. There are many schools of thought on how to design, so just take this as one principle to consider. Design is essentially a process of making complementary elements work together, each one highlighting the other. For example thick and thin, rough and smooth, dark and light, modern and antiquated or warm and cold. Taken too literally you can end up with, for example, equal strips of red and green which is not neccessarily good. But many designers will put a little of the opposite of something in an image. For example, take a night forest scene full of cold, dark blues, and put a fire in one area with light, warm yellows. Alternatively take a sleek, shiny spaceship and put in a small area of rough, dull damage. Each element helps to emphasise the other elements in the image.