Don't make a collection of different types of tetras (1 of each species)
Don't put 6 gouramis (dwarfs and pearls) in a 60 litre tank with little decoration
Don't try to grow plants without dosing nutrients and not having an UGF
Don't put on your lights for 12 hours and expect not to get algae
Don't put cories in a large tank where they have to compete for food with bolder and bigger fish than they are
Don't 'clean' your tank every fortnight, replacing all water and cleaning all hardware and gravel
Be patient in your stocking; don't buy on impulse as it can lead to problems and having to set up new tanks (although this is actually good
)
Don't believe what an lfs tells you.... (9 out of 10 times you know more than they do)
Don't disconnect the hoses from your canister, just close the valves and take off the lid with the hoses
Ensure to have sufficient biological filter capacity, especially if you don't have live plants