Steve:
You and Steve would really only be on the couch if you were watching movies that he needed to catch up on. So, you two would sit side-by-side facing the television and he would put his arm around your shoulders. Sometimes, you would snuggle into his side, but this usually started later on in the night when you started to get tired.
Bucky:
When you two were sitting on the couch together Bucky would sit with his back resting against the armrest and his legs stretched out over the couch. You would sit in between his legs with your back, and head against his chest and he would fold his arms around you keeping you close. Since you two liked sitting this way you had the couch perpendicular to the television, so that you could see whatever you were watching.
Pietro:
Your couch was a sectional, so you sat on one end of it with your legs out in front of you and Pietro would lay on his back across the other section. He liked to lay with his head in your lap and you would run your fingers through his hair, which had a tendency to make him bit sleepy.
Loki:
You would already be sitting on the couch when Loki decided to come over and join you. You would have your back against the armrest and your legs resting on the couch in front of you. Loki would come over and pick up your legs, just enough so that he could slide underneath and rest them on his own. Then he would usually rest his feet on the coffee table in front of him and rest a hand on your thigh.
Clint:
Similar to Pietro, Clint enjoyed laying sprawled out over the couch, resting his head in your lap. The difference being that he lay on his side and he would usually put a small throw pillow under his head, because he thought it would be more comfortable for you. You also, put you hand on his shoulder, occasionally rubbing circles on it with your finger
Thor:
You would definitely sit on Thor's lap and he would absolutely love having you there, so close to him. He would wrap one his arms around your back holding you and you would end up resting your head on his shoulder. He would place his other arm over your legs, with his hand on your thigh.
Tony:
You and Tony sit on the couch facing each other, both with your backs leaning against one of the armrests. You would generally have your legs tangled together, careful not kick one another on accident. This position isn't very cuddly, but it's great for tossing food at each other and trying to catch it in your mouths which makes couch time fun for both of you.
Natasha:
Usually you were already home when Natasha came back from whatever Black Widow task she had been up to that day. You would be sitting on the couch with your feet on the coffee table when she plopped down next to you. Then without a word she rest her legs over yours and give you her signature smirk, as if daring you to push her legs off yours.
Wanda:
You would sit with your back against the arm rest of the couch and your legs would be out in front of you, occasionally with one of your feet hanging off. Wanda would lay down between you legs, on her side facing the television. She also used your chest as a pillow and enjoyed holding your hand while she was there.