Important guidelines you must follow when handling chemicals
When adding any chemicals to your skimmer basket ALWAYS make sure there are no traces of another chemical in the skimmer basket before adding it.
NEVER, NEVER, NEVER, mix chemicals. When adding chemicals to your pool allow one to disappear before adding another. Once they're dissolved in the pool they will be fine.
ALL forms of acids react DANGEROUSLY with all forms of chlorine or bromine. NEVER mix swimming pool chemicals of any type! Chlorine compounds that look or smell alike may not be the same: you have to know the actual chemical. Allowing even small amounts of different chlorine sanitizers to touch each other can be REALLY dangerous. In particular, trichlor and calcium hypochlorite can react dangerously on contact with each other. Once they're dissolved in the pool they will be fine.
Minimize the different types of chemicals you store.
Don't buy more than you will consume in a season. Some of the more hazardous pool chemicals don't keep well.
Keep wet hands and dirty scoops out of your chemicals. Contamination is often a cause of problems.
Don't store pool chemicals where other materials can fall into them.
Use gloves and glasses.
Make sure chemicals are locked away from small children.