There are two ways to do this.
Way one: Use a weapon with animation, and a pose like Victory.
I like to do this by using a weapon with an effect. For example, one of my favorite weapons are the Fae one, with the butterflies.
First, get yourself a weapon with animation. You can check them on marketboard. Some are more, some are less expensive – but you can always find something affordable. Some, you can even grind out easily by running a trial unsync for example. But, you can always use the market to see the most popular ones.
Second, make sure to build a glamour with this new weapon/item, through your Glamour Dresser. Once all is done, make sure your Gear Set is set. (This is important for Portraits to work.)
Then go into Portraits, Edit, and just select any pose which has your weapon out. For example, Victory, or Battle Stance. Pause your character, set your expression, create the perfect Portrait.
Way two: By using the special Poses.
Click Display Poses List in your Edit Portrait window:
Pick Job Actions
Some poses are really, really cool. You have to unlock them via PVP, in Wolves’ Den Pier. And that’s it!
I also made a Short about it: https://youtube.com/shorts/g8zHLK3X3-I