Buy at the bottom of roller-coaster stock markets.
Buy on the dips has been my personal mantra for the last 18 months. In roller-coaster stock markets, you don't want to buy at the top of the ride, but the bottom.
The recovery is set to be a long, bumpy and often nauseating ride, but you should find it more profitable if you're buying when the FTSE 100 is plunging towards 5,000 rather than flying near 6,000.
My mantra is now coming into its own, because if this isn't a dip worth buying on, I don't know what is.
The big dipper
As recently as February, we were all feeling giddily wondering what we'll do when the FTSE hits 6,000. This week, it has shaded 5,200.
That means share prices are more than 10% cheaper than just three months ago. Exactly how big a dip do you want?
Actually, I know the answer to that question. You want it bigger, much bigger -- say, 5,000, 4,500, 4,000 -- and are relying on the eurozone to give it to you.
Some of you will be looking forward to the next big lurch downwards, and I see from the discussion boards that some have set a target date of 17 June, when the Greeks go to the polls again. If they reject austerity, or fail to produce a working government, markets could take another ride on the big dipper.
The great bear hunt
Be warned, because a lot could happen in the interim. Central bankers could bring out their big bazookas and blow the bears away, leaving the field clear for the bulls. Germany might finally cave in and let the European Central Bank slash interest rates, print money, issue eurobonds and accept fiscal union. The BRICs might reboot their slowing economies with a dose of monetary easing.
If that happens, you'll kick yourself for failing to buy today. So beware Greeks bearing gifts (or IOUs, for that matter).
Cheap as dips
Don't confuse buying on the dips with timing the market. You aren't trying to guess what happens next, which, as every Foolish investor knows, is an impossible task.
All you are doing is buying shares because they were cheaper than yesterday. There is a good chance they may be even cheaper tomorrow, but they may also be more expensive. You don't know. You aren't pretending you know, either.
Pump it up, baby
I'm not suggesting you throw all your spare cash at the current dip. I'm certainly not. I've been feeding in one-off sums of £1,000, or £2,000, whenever markets dip a little lower.
I've bought units in the SWIP Foundation Growth fund, which has a total expense ratio of just 0.11% if you buy through Hargreaves Lansdown (LSE: HL), plus a £2 monthly platform fee.
There are other cheap trackers to choose from. Here are five of them.
How low can they go?
As David Holding has discovered, the short, sharp bear market has thrown up some big bargains. They include insurer Aviva (LSE: AV), down 25% since 27 February.
Barclays (LSE: BARC) is down 29% since that date, too. BHP Billiton (LSE: BLT) is down 16%. Royal Dutch Shell (LSE: RDSB) is down 12%.
Mining companies Kazakhmys (LSE: KAZ) and Eurasian Natural Resources Corp (LSE: ENRC) are both down nearly 40%.
I think of the shares I bought in last year's dip, such as Smith & Nephew (LSE: SN). The purchase is still in profit, despite recent falls, and I have also pocketed a pleasant yield.
The psychological bit
You have to brace yourself for the fact that any share you buy now could fall further. Provided you have committed to the stock for at least five or 10 years, that is only a paper loss, and you should recover it once the economy starts moving again.
If you're pocketing an attractive yield, it could prove a rewarding wait. And at least you won't have lost as much as if you bought at the market peak in February.
Plus, you can always console yourself by averaging down at an even cheaper price.
Most investors find it a lot easier to buy shares when the big dipper is rising rather than falling. You really have to bully your mind into doing the opposite.
I'm getting there. I talked myself out of piling into stocks in a panic in February. With the underlying eurozone contradictions completely unresolved, I suspected that rally couldn't last.
This is a doozy of a dip, and I'm doing my best to take advantage of it. I'm even downloading reports such as this to find potential winners.
Like you, I suspect markets have further to fall. If they do, I will feed in more money.
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> Harvey owns shares in SWIP Foundation Growth, Aviva, Barclays, BHP Billiton, Royal Dutch Shell and Smith & Nephew. The Motley Fool owns shares in Hargreaves Lansdown and Smith & Nephew.