A few thoughts...
I like this first pix from HGTV and you can find those deer candle holders everywhere.
You can go tall if you keep the eye level clear: example would be a clear vase with tall branches giving height and fill in with low items around the base. Red berry branches would be pretty for holiday.
Different heights add interest to a table
Table overlays adds dimension
When using a nature based theme real vs. artifical adds warmth and harmony (I would stay away from any artifical flowers/greenry - bad feng shui)
Real pine trimmings and candles are combustible. Really.
Unscented candles are best for food tables
Pale seashells/snowflakes make for a nice all white combo
Clear bowls with lots of floating candles
Garden store six pack plants and sod can be your friend
I like to have desserts double as centerpieces at a tea. Also, flowers in teapots and cupcakes in teacups.
Grouping like items can be pretty and simple. For my work dinner I'm toying with the idea of a raised platter of grouped pears all standing up lit from within surrounded with many votive candles and bowls holding the chocolate for my tastings.
Also thinking about red/green apples
We recently did a beautiful event at work with single stem branches of white orchids (these were the inexpensive kind you see at trader joe's) in a collection of various height bud vases and votives grouped together. They were stunning and the all white look made it seem like snow.
http://www.hgtv.com/holidays-entertaining/8-great-holiday-ideas-to-add-sparkle-to-your-season/pictures/index.html