Ok, here's my advice.
1. Do NOT stack them close.
Treat these things like works of art because thats basically what they are. No one takes their paintings or sculptures and just jams them into a little cluster. It makes the display messy and makes the objects in it look cheap. Make sure each has some space of its own. If you have too many to feasibly do that, I would honestly suggest storing some and rotating the collection over time. Believe me, it will look far better that way.
2. Form groups
This is something that can contradict number 1 to a degree. You can put figures closer together if their designs and general style match. Similar colors, similar themes, same artist, etc. All these things reduce the "Clash" which makes tightly packed displays ugly. >>9225881
is a good example of this. Its too tightly packed for my liking, but the general chibi, cute design and similar sizes make it work better than if they were all random sizes and designs.
3. Carefully consider where you place them.
A dedicated display will always look better than the alternative. If you stuff these guys in with a bunch of other toys, they will probably fade into the background unless they are very large or very eye catching. And if you just stick them on an end table, it will look like you ran out of space. If you have a dedicated display case or shelf for them, they'll stand out and look much better. What's more, if you're going to get a display case or shelf I recommend you be careful with its size. Sofubi can often be quite large, you don't want them to look cramped or not fit. Open, wall mounted shelves might be best. Alternatively Plant shelves are actually quite nice. They specifically have lots of individual small platforms offset at different asymmetrical heights. This can force the observer's eye to focus on each figure individually instead of just scanning across them.