Living rooms can be multi purpose and you want to make sure that yours is designed with how you live in mind. Do you entertain a lot? Do you need seating for family or friends and visitors? You'll want to make sure you have seating for either your family or friends/visitors. In terms of how you orient your furniture, you want to consider if you have a view or fireplace you want to use as a focal point. Are you a tv watcher or maybe an art collector?
One thing I love to do in terms of orientation of furniture itself in a living room is to look to the past. Instead of using huge sofas to fill up the space, consider dividing your space into different zones. You see this throughout history including in historical homes. Seating areas that are good for 3-4 people help a space feel cozy and intimate. If you like to entertain, this is a great option. It gives your guests spots to relax and converse. It's not that often that you see a really large group not divide into smaller ones.
In terms of furnishings, if you have hardwood floors or tile, you will definitely want a rug in your living room. A rug will help absorb some of the sound in a space and will make it feel less hollow and will give it less of an echo. Rugs should be larger than you think they should be. What you want to consider for rug sizes is whether or not you want to see any portion of the furniture off of the rug itself. Some people are okay with only the front legs of a sofa or chair on the rug. Others like myself, prefer a rug that has space to hold the entire piece of furniture - all 4 legs on the rug. Don't just consider what a big box store is telling you via an instagram post in terms of sizes. Maybe they don't carry larger sizes. Maybe they are only trying to sell you what they actually can provide you.
I'm a firm believer in tables including when you've divided your living room into separate zones... coffee tables, drinks tables, side tables. Having lots of options for guests, books, candles, decor, etc, are great for the space to make it feel complete.
In terms of colors and patterns, this comes down to personal preference. Some people want to see color and others prefer neutrals. You want to consider your preferences when thinking about your living room decor. Some people want neutrals with one or two colors mixed in. Some people want printed fabrics. There is no right or wrong. Your home and living room should be a reflection of you and your tastes.