When not to follow it: you can save by waiting to buy seasonal goods at the end of the season.
Rule of thumb: buy in bulk to save
When not to follow: when it comes to perishable foods, shelf-stable items such as cooking oils, or non-food items that will lose effectiveness after a long time, it's okay to buy more frequently.
Rule of thumb: don't spend more than half of take home pay on living expenses.
When not to follow it: it is a good practice to spend 50% your take home pay on necessities (housing, transportation, food, etc.), 30% on life style (Cable, telecom, gym, dining out, etc.), and 20% for retirement. But as life events happen, it's okay to adjust your spending pattern otherwise.
Rule of thumb: pay off high interest debt first
When not to follow it: when the high interest debt has a huge balance, it is a more psychological win to pay off debts with smaller balances. Also, if you could save the money to get company 401(k) match, wait to use it to pay off the debt.
Rule of thumb: buying a home is better than renting
When not to follow it: if you want to stay mobile for professional or personal reasons.
Rule of thumb: buy if you plan to stay more than 5 years
When not to follow it: if you live in cities where home prices compare more favorably with renting or appreciate considerably, the five years threshold could be a lot shorter.
Rule of thumb: only buy stocks you are familiar with
When not to follow it: a good product doesn't mean a good investment, more research is still needed even you like a company's products.
Rule of thumb: dollar cost averaging is the best way to invest
When not to follow it: if you are investing for the long term, invest a lump sum all at once is better than dollar cost averaging investing, because stocks perform better than cash over the long term.