When shopping, start with color. I usually go neutral for my wood fired pots, then sometimes one bright color to make it pop.
When you get home, set the entire thing into a vase with ice water until you have time to take on the bouquet.
When you’re ready to arrange, pull apart the entire thing. Pick out a big focal flower (probably the biggest, prettiest one,) then start pulling from the rest of the options to build out from that one flower. There is a rule of threes in the art world—if you can use three of those focal flowers, it tends to make the aesthetics “work.” Use some of the fillers between the focal flowers. Start to build the bouquet in the palm of your hand.
As you add to the bouquet, play with the height of the various flowers. See what looks better or worse as you play.
Look at your vase. How wide is the opening? You want your handful of flowers to fill most of that opening, or the entire thing will splay out and have gaps.
Once you’re happy with the size of the bouquet you’re holding, it’s time to decide what height at which to cut the flowers. Set your chosen vase at the edge of the table. Hold your handful of flowers next to the vase, and squat down to look at it from the side. Raise and lower the bouquet to see what works with the size and height of vase you’re working with. Cut all of the stems at a 45% angle at that length (I go a little longer than I think, then cut again once the bouquet has a trial run in the vase.
Plop those flowers in the vase, step back, and admire! Trim shorter as needed. Pull off a bunch of the leaves on the stem, to keep them out of the water. If your bouquet is in a handmade vase, pull off any leaves that are hiding the lip of the vase too!
To keep your bouquet fresh, change ice water every few days. Trim the stems a bit too.