First of all, we are not talking about your regular scheduled contributions to your 401(k), 402(b), 457(b) or IRAs. For those contributions either every paycheck period or your own schedule, you allocate the money to buy funds. You should continue to contribute to your retirement accounts without fail. You should never time the market with your retirement savings!
This is not what we are talking here! We are talking about the extra cash from selling a property, receiving a cash gift from your parents, etc. How do you put the cash into the market?
In the current volatile market, you need to wait for an entry point to get into stock market and bond market. The entry point would be either a recession or a correction. With Trump pro-business policy, we don't see a recession in the horizon.
A correction is the broad equity market down about 10% from its high, when we say the broad equity market, we usually refer to S&P500 Index. But in the current market condition, I would say that a correction is S&P500 Index down 15 to 20%. S&P500 Index reached the high of 2,931 on September 20th, 2018, 15% pull back will be around 2,491 level. If you want to put the money into the market, you can put the money into the market with a dollar cost average method.
When investing in bond or bond funds, you need to pay attention to the duration, you should only invest in bond funds with < 1 year duration because we are going through the rate normalization process. Federal Reserve Bank is going to raise the rates one more time this year. If you invest in a bond fund with the duration of 6 years and the yield 3%, you will make 3% return and lose 6% when the rate going up 1% which is very likely this year, your total return for the bond investment will be -3%. Good luck.