While I don't have a ladder shelf, IMO the way to decorate any style of shelf is to use a variety of items, shapes, sizes. I always like to see some books but that's likely my bias as a reader! Also rectangular baskets work well on lower shelves.

Here's a pic I found on Pinterest from the site linked below. There is a nice mix of items on those shelves.

Here is a link that might be useful: white wall shelves

I will have one in a guest room. On it I will keep maps, day trip books, a coffee maker and supplies, drinks, snacks, soaps/shampoos/towels/ sewing and pharmacy needs, etc. I haven't set it up yet. Before, we kept it in a family room with games, books, etc.

So - not really decorations, but I really like the varied shelve sizes.

Lucky, that's a pretty shelf! We have a lot of books so maybe I can find a few that would look good on it? The eyes go straight to the shelf when walking from the front door to the kitchen.

Nightowlrn, What a perfect use for it!

I put 2 in my 10 yr old sons room when I redecorated it last year. I didn't realise they were trendy until just now. They happened to be the exact measurements I needed for the space. It's funny how many times I buy something thinking I've found something cool and then realize later that I just followed another trend. Lol.
He uses them to display completed Lego sets but I'm sure that's not what you have in mind ;-)

I have one in the back of my older son's closet for shoes. They aren't my favorite decor item. Suggest if you use one that it is mounted in some way. They can easily be pulled down and an accident happen. Especially if the items on shelves are not balanced for weight to the shelf.