Which mutual fund should I buy?

If you are absolutely new to the world of mutual funds, you should probably choose four funds to begin with, two from "normal-risk" funds and one each from "lower-risk" and "higher-risk", all in equal ratios. You should invest regularly through SIP ( Systematic Investment Planning). For example, if you can save Rs.4000 each month, put Rs.1000 in two funds from the Top 7 in the "normal-risk" category, and Rs.1000 each in "lower-risk" and "higher-risk" category.
As you become more familiar with investing in mutual funds, you can try the "highest-risk" funds. Be careful in investing in them though. If you look through the complete funds list, you will usually find that the highest risk funds occupy all positions at the bottom of the table.
And please remember, never ever stop your SIP investments when the market goes down.

Which mutual fund should I sell?

You may need to sell a fund for two reasons - the fund is not performing well, or, you need the money. Refer to the full rank page. In case of normal, higher, or highest risk funds, any fund with a net rank poorer than 100 would probably need to be sold. In case of lower-risk funds, sell if rank falls below 150. If you are selling your fund because you need the money, sell units from funds with better net ranking, but poorer monthly rank.

How do I save tax?

If you need exemption under Sec. 80C, you need to invest in ELSS (equity-linked savings scheme) funds. ELSS funds are normal risk funds, however, their performance seldom match plain funds. They have a lock-in period of 3 years. Click here for ratings.