I caramelized a giant batch of onions two days ago and I can still smell it! 
Just looking for ideas to make my house smell better.
I get some really nice incense on the cheap from a nearby store, and I also have one of those wax melty things, though I’ve noticed that the shelf life of a given chunk o’ wax isn’t all that great. I may switch to scented candles.
Open some windows.
Also, when I used to have a deep fryer, I learned quickly that the trick to not having my house (or rather apartment at the time) smell for days after using it was to use it outside.
Find sources of bad smell and get rid of them.
My wife sprays Thieves oil when the house gets stale smelling.
If you can’t open the windows, then spray Ozium (original scent). Works a treat for eliminating cooking odors.
I clean the floors often with lemon scented Mr. Clean.
Friends gave us a set of Rituals bath stuff that included areed diffuser. It smells a lot better than most reed diffusers (most make the whole house smell like a toilet), but I find it too strong.
I like incense, but we can’t have it because of my SO’s asthma.
I’ll harvest some lavender in a few days, hang it in little bundles.
Open the windows, burn some candles.
My “in a pinch” air freshener is to toss some citrus peel into a saucepan, add water, cinnamon, and vanilla extract, and simmer for a couple of hours. Nice smell, not overpowering or chemical.
Wow, one of the best ways I can imagine to make the house smell better (or at least more appetizing) would be to caramelize a big batch of onions 
Given that’s the smell you’re trying to get rid of though Lacunae has some other appetizing smells advice.
Embrace the aroma of caramelized onions.
My MIL swears by this. Her home always smells like something is baking in the oven.
You can buy little scented “tea candles” in a pack of twelve cheap. They burn for about 4 hours.
Febreeze anything that smells funky 
I don’t aim to make my house smell good, I just keep it from smelling like anything at all. Cats willing, of course.
I ask my husband to make bacon.
Incense. Much cheaper than scented candles and carries a lot of positive associations for me. Always puts me in mind of old book stores and record shops. I always have several different scents around and like varying them up.
Gave away the cat that started pissing on the carpet in the garage. And, sometimes behind the couch. And under the dining room table. Made all the difference.
Truth to this…I get mine at the dollar store across the street. That’s $1 for 16 tea-size candles. Bonus- you never clean wax out of the votive candle holders. Just toss the old metal cup and begin anew.
It likely has coated the walls and other surfaces. Wipe down the whole interior of the house with Lysol.
I buy a pineapple cheap. stand it on a saucer and place it in the hall, and let it moulder for a few months. Then I throw it out for the birds and buy another.
I’ve never heard of this elsewhere, but it’s a refreshing scent.