Colour, value, form, shape, space, lines and textures are the elements of design. Proportion, balance, movement, emphasis, variety, contrast, unity are the principles to apply to the elements in any work of art. After all you are creating a masterpiece when decorating a tree! Remember, you are the master/mistress of this project. Don't let anyone tell you what it should be, including me! These are merely suggestions, recommendations from over 15 years of experience. There are always exceptions to any rule.
I've found that for the sake of simplicity and to eliminate guesswork, I don't use more than 3 colours maximum and keep them of a similar lightness or darkness (value) so it looks "together" (unified). In the process of selecting I always have more of one dominant colour (emphasis), a bit contrasting colour will pack a punch of WOW. What pulls it together are the metallic ranges. I find silver works best with the cooler colours of burgundy, purple, blue or winter white. Gold (and there are so many shades!) adds to the warmth of reds, ivory, sage green, and even orange! For a truly coordinated effect, chose tones that will compliment your current décor. Our home is turquoise as you may already know from this previous POST LINK which is my accent colour against silver and ivory for an elegant classy look. It may not "fit in" with country living but it's my tree and I love it!
The same applies when selecting textures, sizes, shapes. There needs to be a dominant one. Textures can range from sparkly, shiny, satin finish, velvet finish, soft & fuzzy, or prickly. Shapes also play an important part and much like designing a floral arrangement, you need round item such as balls, dried hydrangeas, bows or fruit for example. The spiky items are stars, pinecones, birds, even teddy bears where shapes tend to stick out every which way. Your linear decorations can consist of things like feathers, garland, ribbon which will break up the visual of so many chunky ornaments. Curvy lines will create movement and cause the eye to move all over the tree literally captivating your audience! Plus it's just easier on the eyes. And finally in our special case, "danglies" as I like to call them include icicles, tinsel, chandeliers and mainly vertical decorations. All of these shapes can also be of a certain texture. A small red velvet teddybear would cover your red, soft and spiky quota. A dried ivory coloured hydrangea handles the larger round shape, rough texture and lighter more neutral colour. Silver mini chandeliers add the shine, and dangly character in a metallic tone, and so on. For unity, I find it's easier to pick a theme whether it's rustic, elegant, children's toys, candy, fruit, nature, birds and whatever you can come up with.
Tip: Use odd numbers of ornaments; 3, 5, 7, 9, 11, 13 etc....
Use the rule of 3's for a pleasing balance i.e. one third amounts of textures, shapes etc., while keeping one dominant (or 2/3)
Tips: Place smaller shiny ornaments deeper inside the tree to reflect the lights especially if you skimped on lighting.
I start with the largest ornament (hydrangeas below), spreading them out evenly around the tree. The next bunch of ornaments are my finial shaped in the dominant colour that will go in a diamond or zigzag pattern evenly spaced. Then my modgpodged newsprint balls went on, followed by the clear galss balls. These are the ones that can be tucked inside to reflect light. Macrame snowflakes went on next, with turquoise accent colours to break things up. The "danglies" were hung and afterward my tiny chickadees. It's important with birds, to point them in various directions for a natural feel. Lastly the ribbon garland gets laced through the tree, weaving in and out , over and under LOOSELY so the tree doesn't look strangled.
Lastly, for an elegant finishing touch, I prefer to use a plain piece of substantial fabric for the skirt. Gold or silver lammé works well but even better is the liquid like metallic fabrics as seen here. To save money, choose the metallic colour which can be reused after you tire of the accent colour. You need 3 meters or 3 yards to have enough to cover the base with some looseness for folds. NO hemming need, just tuck under any rough edges and you are ready for presents! The added bonus is you can recycle the fabric later. For extra pizzaz you can match your wrapping paper! Now everything is a go!
I hope you learned something new or were inspired. Wishing you lots of fun decorating!