I like to keep this chart handy because it shows seasonality for the bull market that started in 2009. It's helpful because it shows common turning points and seasonal trends. The x-axis is the trading day of the year and the y-axis is the percent gain for the S&P 500.
One useful observation that is pertinent to the current time of year is that the market has never been down once if you bought on March options expiration and sold a few days into April. After that, things get a lot more choppy into the summer months, although I have reason to believe things won't be so bad this summer for stocks. There is still a lot of negativity about the market.