for a proper big clean:
1. turn everything off
2. take out ornaments
3. gravel vac till you have 1 bucket of water
4. wash out filter media in this bucket of water, if using carbon more than 4 weeks old, replace or disgard
5. check filter impellers are not jammed or clogged up
6. take apart filter, give it all a swish in the water
7. whilst you are doing all this do not let filter media dry out, keep it in the bucket
8. chuck away that water
9. carry on removing water and gravel vaccuuming till you have taken out 2/3 of the water
10. do not gravel vacc more than half the gravel
11. fill up bucket with clean water, mix both hot and cold so you have the same temp as your tank water
12. add water decholrinator and any plant food, meds or salt you are using to the bucket
13. add the water slowly to avoid alarming fish
14. repeat till tank is full
15. add decorations back in
16. turn everything back on
17. wait 10 mins, then give fish a small treat
ooops i forgot - clean tank sides. that should be number 3, so that then the gunk is removed during the water change