It might help to make note of where the empty space should be after you have completed the slider:

Perhaps work on the top left corner of 4 tiles first, then the top right section, then the bottom right section, leaving the bottom left section with the empty space until last.
ronrob posted this very helpful tipsheet on how to solve sliders, perhaps it might help:
If I know what the completed puzzle is supposed to look like, my technique with sliders is to line up what goes into the first row in the last column. For example if the first row is A B C D, then I create
X X X A
X X X B
X X X C
X X X D
Then move the tiles out of the first row and snake the column tiles counterclockwise into the row.
If the second row is J K L M, then I create
A B C D
X X X J
X X X K
X X M L
Now move the tiles out of the second row and snake the column tiles counterclockwise into the row.
A B C D
J K L M
X X X X
X X X X
Etc.
Again, this assumes you know what the final product looks like. If you don't, slider puzzles can be very difficult.
