Debits and Credits for different transactions

Ok, first off, there are essentially two categories of transactions, we have your:

1. Balance Sheet Transactions:
Assets - stuff you own, makes money for you (GOOD), etc like buildings, inventory and cash
Liabilities - stuff you owe, gives you money (GOOD) to buy assets but you have to pay it off later (BAD) like bank loans, supplies bought on credit and credit cards
Equity - your own stuff you put into your business, i.e. your investment, this creates a your share in your business. you can share your business with other people in exchange for them putting money into your business but too many shareholders can affect control of the company (UGLY).

and

2. Income Statement Transactions:
Income - Sales, rental income, investment income - basically anything that puts money in your business (which IS NOT from a loan or equity)
Expense - Salaries, Bills, rental expense, cost of materials - basically anything that takes money away from your business

To keep it really simple, just remember the following:

ASSET - increase=DEBIT, decrease = CREDIT
LIABILITY - increase=CREDIT, decrease = DEBIT
EQUITY - increase=CREDIT, decrease = DEBIT

All INCOME is CREDIT
All EXPENSE is DEBIT

For a more detailed explanation, check out the Golden equation and Debit and Credit slides in the previous post.