A neat, attractive lawn adds a great deal of curb appeal and is something you can do yourself, sometimes at little cost to you. Plant some shrubs, put down some mulch and clear out any brush or dead plantings. Get a power washer and wash down the outside of the house, your driveway, steps, any patios and/ or decks..you can even paint if needed.

Basically, do little things that will attrach people to the house, giving them the impression that it is somewhere they would want to make their home. Also, if you are selling, light scented candles to create a warm and cozy atmosphere. People relate good scents to good feelings.

Hope this helps!!!
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Having said that, a touch or two of greenery here and there is always nice and homey. Do you have a few family photos displayed? If not put a few of them around - they make for great conversation starters.
How about a lap throw on the couch, a few throw pillows? These are especially nice without adding to a clutter problem.

Best of all, add a personal touch for your houseguest. Get a large cheap basket (Walmart? Michaels?) and fill it with fresh towels, scented soap, a new tube of toothpaste/toothbrush (just in case they've forgotten) a few books that may be of interest to your exchange student, chocolates…whatever touches would make an overnight guest feel welcome. Place the basket next to the bed/couch/sleeping bag where they'll be spending the night, and make sure they know it is for their use.

Don't forget fragrance. Have a crockpot or large saucepan with hot apple cider* bubbling, with some cinnamon sticks and glazed cookies waiting to nibble on. The apple cider makes the house smell WONDERFUL, and can be as inviting as any expensive makeover.

Of course, long after the memory of your rooms has faded (and let's face it, that won't be for long) what this exchange student will remember is the attitude of those they stayed with. Were you all welcoming? Did you make him/her feel at ease? Did you think about their personal comforts/interests while they stayed with you? Did you make them feel special?

I think it's great you all are opening your home to an exchange student, and that you want to make everything as cozy and inviting as possible. That speaks volumes about the type of home you have - I think this is one fortunate house guest.

Have fun -

*Hot apple cider recipe

Large container apple juice
1 small bag cinnamon red hots
1/4 cup orange juice

Mix all ingredients together, stir occasionally over medium heat until the cinnamon hots are melted. Simmer on low and serve throughout the evening.
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Sincerely;

-Trux_Dea