Improving your fortune is basically talking about your financial situation though you could interpret it to mean your general position in life outside of money. We're kind of taking both approaches here on this page. Hopefully they'll suit your personal circumstances.
As the Tree Grows
As a tree grows, so will your fortune with this spell. You'll need to have a tree nearby you can access, and it's hopefully private enough that you can leave a small charm bag without someone taking it down. Rather than a local park, try the woods if you don't have a yard with trees of your own.
On the piece of paper, write your name out so the letters for a circle. Draw a small pentacle in the center. Fold it up to fit inside the charm back. Draw a pentacle on the acorn and the stone, and put them in also, then the coin and feathers. Tie it up tightly, and hold the bag between your palms. Repeat:
As the tall tree grows,
So does my fortune.
As the sun rises high,
So does my fortune.
By this charm, I do begin
Magick starts to grow within.
Take it outside and find a private tree. Loosely tie the charm bag to a branch as high as you an reach and repeat the words again. After that, new financial success will start to come your way but it can take a little way because trees do grow slowly after all.
Make a Fortune Candle
This is a bit more of a DIY spell than most, but if you're handy, it shouldn't be a problem. Though it uses a number of coins, it will help bring all sorts of good fortune, not just money.
I'm not going to give you all the instructions on how to make candles. You can do a little Googling yourself to get the details. The trick to making this a fortune spell candle is the added coins and herbs. When you pour the melted wax into your mold, mix in the herbs and drop in the coins one at a time. Make sure there is some wax between the coins so they're not all clumped up.
When the wax is set, you now have a homemade spell candle. Use it other spells, or simply light it on its own when you need to boost your fortune.