
Hi Limeyron.Anything that has surface area can host good bacteria-gravel/ornaments,plants,etc.They are in the very small range though of holding it as your filter is really the big space.
I do weekly water changes,along with gravel vacs.If your tank is pretty new and still trying to establish itself,then you can do a gravel vac on half the tank's gravel at one time.As for plants/ornaments,etc,I only clean them when they are getting alot of unsightly algae.I take them out of the tank and soak them in a Vinegar /water solution in very hot water,and I buy a nice soft bristled toothbrush to clean the ornaments with.Once I get them clean,I rinse them over and over in water.Some people use Bleach the same way,but I don't feel comfortable recommending Bleach to newbies.Anytime that you have ornaments,etc.,it's always a good idea to pick them up during weekly gravel vac's and clean under them.It's amazing how much gunk squeezes it's way under them and builds up.By moving often and cleaning,you'll have alot less problems further down the line.
Sometimes tank glass gets that white slimey algae/or brown fuzzy appearance.You can buy a brush at your local fish store to scrub the tank glass with to get that off if it's bothering you.I tend to go to the Dollar store and buy a pkg. of these plastic like "scouring pads" and keep one at each tank area,for this reason.I normally clean the front and the sides and leave the back alone,unless it's getting rather unsightly.
Cleaning my filter's depends on what type they are.Aquaclears tend to rise up when the filter sponges get dirty-which can sometimes cause water to be on the floor.

I tend to take them out during my water changes and swish them around in the water I just changed out,to get any major gunk and such off of them.My tanks have been established though for a long time,so I never have any bumps in my cycle doing this.As for the Emperor's/Penguin Filter's,I do those less often,probably every couple of weeks,and I give it the same treatment as the Aquaclear sponges.By doing this,it also helps keep your Nitrates from going sky high too.If you ever see the water just trickling out of the filter,or parts not flowing smoothly,then that's also an indicator that your filter needs a good rinse.Hope I helped you some.If you have any more questions,feel free to ask.