About cooking:
You can kill your enemies easier than you think.
Just feed them Arsenic which is hard to detect on dead bodies.
About cleaning:
When you're done dismembering a body, make sure you clean with hot water and bleach. Be sure though, to wear a gas mask, as bleach reacts with hot water creating nasty and toxic fumes.
About gardening:
When you bury your victim, make sure you plant endangered plant species so it becomes illegal to dig up your victims.
About washing:
Make a mix with Baking Soda, Lime Juice and vinegar. It will not only get rid of blood on knives, but it's something I clean metal with in order to eliminate rust and oxide on blades/saws.