Do nothing for the first week. Park the money in a savings account and resist every urge to spend, invest, or lend it.
In the first month, clear high-interest debt and build an emergency fund of three to six months of expenses.
Spend months one to three learning the basics - ISAs, index funds, pensions - before making any big decisions.
After three months, put the money to work: max out your ISA, consider a pension top-up, and keep the investment strategy boring.
