Other than the usual suggestions of checking in settings that you're updated to the latest software I'd recommend a few things that could help or could be a waste of 15 minutes or so but always worth a try.
After every update I wipe the cache partition (easier to watch quick YouTube video than me explaining the process) because people say to do it, I don't know exactly what it does though. I also clear the cache and the app data in the camera app itself (after every update) by holding down on the app then hitting the i in the top right corner, you'll get the options there. Note though that deleting the data will in a sense reset the camera app saved settings so if you spent a lot of time configuring and customising the settings/button layout it's probably better skipping it. It will be like the app was when you first opened it.
Then I use the app "good guardians" to utilise the galaxy app booster (I actually do this before and after cache wiping and no there's probably no reason to do it twice and I'm not sure if it affects camera performance or rendering but it's good practice I guess).
That's about it. I don't use the high MP mode very often unless I need a very detailed shot. I don't put anything over the lenses to protect them. A colleague of mine got the phone and put on a glass protector and it made the pictures she took weird but she could have put it on wrong or not cleaned it properly I don't know. Microfibre cloths are a must for me and I clean my lenses and screen religiously. I also stick to 1x 3x and 10x zoom only. I find it is muted on the inbetweens and especially from 0.6 to 1x.
Oh and just to round out the OTT unnessessariness I do a hard reset which is just holding the power button and volume down until it restarts.
