I have 3 indoor cats and people say this about my home!
I vacuum and mop every day. I make sure to wipe all surfaces at least once a week, I find dust holds smells... But that may be in my head.
I have a Lampe Berger with the scentless liquid. It genuinely eliminates smells rather than covering them like horrible air freshener. I light it in the morning for 30 mins and after cooking dinner for 30 mins.
I buy sofas from IKEA that I can take the covers off of and wash. I do this quarterly.
I wash all bedding weekly and air out the duvet and pillows. I also use mattress protectors I can machine wash so the mattress stays fresh.
I air out the house for at least an hour, even in winter.
I make sure I clean the extractor fan and change the filter or the smell of old oil can linger.
I wash all kitchen cloths every few days. I don't think people realise how musty and horrible they can get (my mum).
I also make sure the cats have their teeth cleaned and don't have any plaque build up. Pet breath can really smell.