If you wish to avoid capital gains tax on the sale of property, (20% for long term) you could use the funds from the sale of the property to purchase new property within two years from the date of sale of the first property. Don't use those funds! All you need to do is to keep the proceeds in a separate designated account with a nationalized bank till you purchase the new property. However, this exemption is applicable only with regard to residential houses and will not be applicable for sale of a plot of land or commercial property.
Prior permission of the Income Tax department is necessary if the value of property being sold is more than certain limits (usually Rs. 10 lakhs for most cities. The ascribed value is more for the metros). Permission is to be obtained by Filling Form 37-I with the IT department.
Application for repatriation has to be made to the RBI within 90 days of the sale of the property.