First pick a theme and style. Looks like nautical or aquatic could definitely work here. A theme will help you restrain your thinking and shopping. It will also help you narrow down materials (I say go with wood and color (blue-green, light wood).
Aside from the theme, looks like the biggest issue is balance. There is too much "white space" and inbalance.
You have a few options, all of them involve better use of balance:
The picture is way too small for that space. It's being swallowed up by the white space. You need a much much larger size frame and photo that takes up at least 50% of the wall space. If you can't find a good nautical theme photo, think about something a bit more statement-y like a nautical wall sculpture. I like the fish idea because then the "white space" at the top of the triangle gives impression of deep ocean and doesn't feel like random space. So a photo or wall sculpture of fish could help incoporate the weird white space at the top into the statement.
You can also hang a bunch of random things/sculptures all around the space like baskets and shells or whatever you want.
Another thing you can do is remove the picture and place the aquarium in the center of the space with two tall plants or trees on either side.
The furniture is very dark and non cohesive. You should just replace it with a set that matches. Or better yet it's really the round table that doesn't match. I would get a new table that better matches the theme or the seating. Same with the aquarium stand.