Before you take out a loan
The checks worth doing before you sign anything, so the payment still fits in a bad month.
A loan is only affordable if it survives an ordinary bad month, not just a good one. Test the payment against your real numbers with the Can I Afford This? calculator, and see what paying a little extra does to the total with the Extra Payment Calculator.
Understand the offer
Read past the headline rate before you compare anything.
The true cost
Compare on total repayment, never on the monthly figure alone.
Your own numbers
Decide from your figures, not the lender's example.
Before you sign
The last pass, done calmly with the paperwork in front of you.