Narrowing down a theme for your wedding is extremely difficult; you take inspiration from things in your life and from you fianc's life, from all the beautiful weddings you've seen to date, magazines, bridal shows and events and then finally your budget. Once it's all planned out and you go shopping, you're tempted more than once to change your theme because of all the gorgeous centerpieces that you find.
It's literally a struggle with you trying to pick out a theme and then trying to stick to it. A great way to incorporate different themes and make shopping for your wedding easier is to give your tables their very own themes. People usually give the wedding an overall theme but you can actually make your wedding arrangements a lot more interesting by giving each table a unique look. You can pick out whatever you like and transform your table according. You can make the tables for immediate family different and the guests can walk around to see all the different themes that you have.
Make sure you keep neutral colors as part of the color scheme and that will make the centerpieces even easier to manage. You can have flowers at one table, candles, fruit bouquets, and fresh fruit arrangements at other ones. It will make it even easier to create the seating plan. Unique wedding arrangements don't necessarily have to work in a uniform matching pattern. You can highlight stages of it by changing the shades of the color you've picked out. Use lighter shades for the ceremony and darker ones for the reception.