Classify an account by what it represents before deciding whether to debit or credit it. Assets and expenses normally have debit balances. Liabilities, equity and revenue normally have credit balances. A normal balance describes the usual side; it does not prohibit an unusual balance.
Contra accounts run against the related account. Accumulated depreciation reduces equipment and normally carries a credit. Owner's Draw reduces capital and normally carries a debit. Sales Returns reduces sales revenue and also normally carries a debit. Prepaid insurance is an asset until coverage is used. Cash collected before work is performed creates unearned revenue, a liability, even though the bank balance rises.