Diversification across bonds, cash and stocks and across currencies and across managers and mainly with large, bank backed managers well ranked by eg Morningstar: you might not do as well as some, but you should be partially protected against inflation, stock market collapse (a la Japan for 20 years) and currency debasement with lower variation in earnings but slightly lower earnings than many other people but you should also have smaller losses than most people who take a less diversified approach when things are "hitting the fan". You will never regale your friends with stories about how you made it big time, but nor will you weep as you explain to your family that you have lost half or all your money or even your house as some people did in Australia in 2007/8 through geared investing through Storm Financial. In Australia simply investing in a balanced fund with a bank owned fund manager or industry super fund is the easiest way to do this, but check the management charges and fees and try to get into the wholesale rather than the retail funds. Beware high entry fees and any exit fees.
The strategy above is essentially a "set and forget" or "buy and hold" strategy with little time commitment and only average returns but relatively safe compared to some other strategies.
More risk means bigger profits if you are right, but bigger losses if you are wrong. If you are young and the amounts are relatively small at present you have time to recover, but if you are already retired or nearing that age you might want to be more conservative.
The following approach would not be recommended for 70% to 90% of people. It is too complex and time consuming and the amounts involved need to be large to make any appreciable difference in dollar terms. Most people would be better off working a bit longer or having a part time job for a while, even mowing a few lawns for neighbours or similar during retirement.
As above but time your entry into different asset classes based on recent performance of that asset class, then be prepared to review things weekly and on occasion rebalance your portfolio across asset classes depending on what has enjoyed a substantial rise and what has fallen and learn the basic buy and sell signals for stocks, bonds and other asset classes in which you invest.
To do this you need to take a fair amount of time to develop expertise, or take a big gamble on an active manager by giving them a broad discretion across multiple asset classes. Consider learning about signals of major changes in trends such as moving averages etc. See:
for some hints about what you might look for.
The following approach would not be recommended for 90% of people. It is much too complex and time consuming and the amounts involved need to be quite large to make any appreciable difference in dollar terms.
If you are prepared to devote the time to do all the above you could also consider whether you wish to engage in technical and fundamental analysis of individual economies, asset classes, stocks and bonds, but frankly this would basically be a full time job and not worth it unless you have a very large amount of money or a real passion. Be aware that changing assets very frequently costs lots in commissions and transaction fees and buy/sell spreads.
This is not investment advice as I don't know your circumstances or even which country you are in or how much you are talking about. Consult a financial planner, preferably one who charges by time and rebates all fees and commissions. The cost might seem like a lot but it is often worth it as they can often assist in ensuring you reduce tax or maintain entitlement to social security/pensions entitlements- but remember the responsibility is yours and you need to monitor your own investments if they are significant.