Try to buy ETFs rather than stocks. Start by selecting 3-4 ETFs which are at its low and buy them. Make sure they have good volume.
You should hunt down MFs when market is down. Be an opportunist and buy as much as possible in low NAVs when markets are down.
Modiefied SIPs gives more if you steadily increase your SIP amount, say by 5 percent every year or quarter.
Stay invested obviously as the more time you give the more fruits you will get (compounding is sweeter when it gets old)