There are two parts to this: getting ten items is pretty easy, just use TOP:
SELECT TOP 10 columnname FROM table ORDER BY number asc
Note that you can't use the GROUP BY clause of your example, because if you do you can't use ORDER BY unless that column appears in the GROUP BY clause. This may help:
SQL GROUP By and the "Column 'name' is invalid in the select list because..." error[
^]
Getting the next ten is more complex:
SELECT columnname FROM
(SELECT ROW_NUMBER() OVER (ORDER BY columnname ASC) AS RN, columnname FROM table GROUP BY columnname) j
WHERE RN BETWEEN 11 AND 20