Unique Totals: Look for cell groups that have unique answers - e.g. two cells totalling 3, 4, 16 or 16; three cells totalling 6, 7, 23 or 24.
Hanging Cells: Look for "supercells" (3x3) which have one unknown (a cell belonging to a group which exits the supercell) - e.g. a supercell completely contains three groups of 9, 8 and 24 and a cell from group which goes outside the supercell; because the supercell has to total 45 the "hanging" cell must be 4.
More Hanging Cells: Look for rows and columns with one unknown - the rows and columns must each total 45 too.
SuDoku: Don't forget to use normal SuDoku rules, if you have a horizontal pair total 17 in the top row of the first supercell and another hpair total 17 in the bottom row the the second supercell, the 8 and 9 must be in the middle horizontal three cells in the third supercell.
Downsize: If you know the value of one cell in a threesome, the total of the other two is the remainder. This is obvious but I find it useful to change the printed cell total value.
Split:. Using SuDoku rules you can sometimes prove that (for instance) two cells in a group of four must be a 4 and a 5 but you don't know which is which. Split the group of four into a two-cell group totalling 9 and a two-cell group for the remainder.
Go Large: I print the samunamupure as large as I can (a single puzzle on an A4 page) then I write valid SuDoku numers at the bottom of a cell and valid samunamupure numbers at the top of a cell (obviously the cells actual valid numers are the intersection of these two).
Party on: Whereas normal SuDoku seems to be a solitary puzzle, samunamupure are REALLY fun solving with a friend. Print a grid each and chat as you work. You'll often find that you miss something that your friend sees and vice-versa. Once you've done a few together you are more in the mindset to tackle one on your own.