Most brokerages (including Vanguard, my personal favorite) offer some form of automated investing. Just fill out a short form instructing the brokerage to withdraw a certain amount from your checking account each month and use it to buy shares in a certain fund.
Automated investing is incredibly great. It has two terrific benefits:
- You can't screw it up—you're no longer on the hook to remember to invest every month. Similarly, since your money's being deducted from your checking account automatically, it won't accumulate there and tempt you to spend it.
- Knowing that you'll regularly be investing a fixed amount lets you intentionally and unerringly calibrate your savings rate. This also ties in nicely with the “reverse budgeting” strategy.
401(k) contributions, by the way, are my favorite form of automated investing, since the money never even hits your checking account. It's easy to forget that you ever earned it, thus removing all temptation to spend it.