LONDON -- Investing doesn't have to be a full-time job -- or even the thing you're most passionate about. (Though if it is, we may have a spot for you at The Motley Fool!)

The truth is, you're busy. You love your money. You've worked hard for it and don't want to watch it idle away in a bank.

But you probably don't want to obsess about it day in and day out, either.

If this sounds like you, you may be a set-and-forget investor. This means you want to find and own shares in the types of companies that provide a good mix of portfolio stability, peace of mind, and extra income.

Let's take a closer look.

Size and stability
GlaxoSmithKline (LSE:GSK)  is a massive, 72 billion pound company with a long tenure in the pharma industry and a strong history of returning cash to shareholders. Though not impossible, wild share price swings in a company like Glaxo are unlikely.

In fact, since July when I first mapped out the five stocks for busy investors, Glaxo has essentially been flat. The FTSE All-Share, by comparison, is up 14% over the same period.

Did I get it wrong?

Not necessarily. Glaxo likely hasn't caused shareholders many sleepless nights because the share price has been so steady. It also consistently throws off a lot of cash in the form of dividends.

In 2012 alone, GlaxoSmithKline returned 8.8 billion pounds to shareholders through share buybacks and dividends. It currently pays about a 5.1% yield, edging out the pharmaceutical average of 4.8% -- and leaving your savings account rate in the dust.

So, what shareholders may have missed in share price appreciation, they've made up for -- in part -- with quarterly dividends of about 17 pence per share.

Consistent and growing cash flows and revenue
Set-and-forget investors can be well served looking for recession-resistant companies for their portfolio. I plucked Unilever (LSE:ULVR), a consumer staples giant with an incredibly steady business, for this very reason. People need the products Unilever sells (think soap, washing-up liquid, margarine, and the list goes on).

Unilever has an established position here in the U.K. as well as a growing presence in emerging markets. With a diverse range of products being sold worldwide, Unilever has a solid, tenured business that puts up consistent cash flows and pays a reliable and well-covered dividend yield (currently about 3.4%).

If you'd set-and-forget this one in July, you'd have seen a nice 18% increase in your shares, plus you'd have received a near-4% dividend paid last October.

Competitive advantage, aka "moat"
When I think about a company with a strong competitive advantage, drinks-maker Diageo (LSE:DGE) comes to mind. This company owns a huge range of spirits brands and has a massive distribution network worldwide. It is hard for new entrants to the market to gain ground on -- and chip market share away from -- Diageo.

Shares in Diageo have lagged the market a bit since my last review in July, posting gains of about 11% against the FTSE All-Share's 14% advance. Shareholders were, however, sheltered from any wild swings in the share price -- and rewarded with a final dividend payment of 27 pence per share in October.

Another huge drinks-maker with a massive moat in the nonalcoholic markets is U.S.-based Coca-Cola (NYSE:KO). The shares actually split 2-for-1 in August, meaning for every share you owned before the split you were given two. Adjusting for the split, the shares are down about 5% from July, though a few dividends have been paid out.

Dividends (the common thread)
A theme in the shares I've mapped out for a set-and-forget portfolio is that each pays a dividend. Remember, a dividend paid to you is a real return -- you get paid for owning the shares. Dividends can help smooth out any emotional sweating you may do over share price movement.

After a brutal start to 2012 that saw shares sold off heavily, Tesco (LSE:TSCO) management had work to do. They were clear that they would focus on strengthening its U.K. business while growing as a multichannel retailer in more international markets. It's been a year, and I for one have been pleased with Tesco's progress on those fronts.

Shares have outpaced the market and are up about 18% since I wrote about them in July.

And when it comes to dividends, Tesco's track record is hard to beat. It's raised its annual dividend payout for nearly 30 years in a row, offering income-focused investors a nice yield to rely on.

Pair that with Tesco's foundation in the U.K. and growing business internationally, and this set-and-forget share seems deserving of a spot in the busy investor's portfolio.

If you'd like yet another income idea for your portfolio, then download a free copy of "The Motley Fool's Top Income Stock for 2013."