when you used pageSize=10; than you can use this code
myGridView.DataSource = myDataSource;
myGridView.DataBind();
myGridView.SelectedIndex = 0;
when you click any pager than use
protected void GridView1_OnPageIndexChanging(object sender, GridViewPageEventArgs e)
{
GridView1.PageIndex = e.NewPageIndex;
GridView1.DataSource = dataSource;
GridView1.DataBind();
}