Some inspiration.

Looks as if you're all set for great summer events in your backyard!

I think a small tree wouldbe nice . Would give some shade and make things less barren.
Even maybe a raised (slightly lower than waist height) planter near the end of the patio would add some interest. I'll attach some pics to show you variations on this...

oops here are the pics...

How about a pergola over the eating area with some vines. A covered area for the grill and some extra seating around the firepit. Some trees that will grow up and provide natural shade and if you put 2 about 12 feet apart eventually a place for a hammock. I would have the people who designed the patio come back and put a sitting wall near the fire pit. Then a planting bed along the edge.

I agree with Dar, you need a structure to break up the flat facade. A pergola or covered porch area would help, or even both. It could even be free standing so you don't have to get into the home's structure.

Here are two Ideabooks to get you started
https://www.houzz.com/magazine/spring-patio-spiff-ups-12-doable-diy-projects-for-your-outdoor-space-stsetivw-vs~9000069
https://www.houzz.com/magazine/7-ways-to-create-a-gorgeous-outdoor-room-stsetivw-vs~8613203

I agree with the others, you need some sort of cover. If time or budget doesn't allow for a permanent one at the moment, consider a portable one for this season or until you can get the permanent structure up. Your deck is large enough for at least two seating areas plus a covered area. Take advantage of all that space :)

Adding separate seating areas is the key. Table and chairs, chairs around fire pit, two chaise lounges with a table in between or a high table with two chairs. So people can sit and chat in different areas.

Large ceramic flower pots outlining the patio filled with flowers will add lots of color and is easy to care for.

We have two pavilions on sale! A beautiful timber framed pavilion would really set off your space! Go to our website for more information.
http://homesteadtimberframes.com/outdoor-living-pavilions/