Be patient when using a tile nipper, if you take off pieces that are too big you could go beyond your cut line. Then you'll have to start over. Tile nippers will leave jagged edges on the tile so use them in less visible areas or where you'll be covering it with trim, like around plumbing fixtures. Use a square-notched trowel for setting thinsets on horizontal surfaces. Use v-notched trowels for setting mastics on vertical surfaces.
Trowels also come in different notch depths.
Use one that's two-thirds the thickness of the tile you're setting. If you don't want to invest a lot in trowels, you can get less expensive plastic ones at your tile supply store. Another helpful tool for scooping out adhesives and grout, and for spreading adhesives in narrow places is the margin trowel . Grout Float Groat floats are rubber or foam-faced trowels used to force grout into the joints between the tiles. Use sweeping motions diagonally and back and forth to work the grout into the joints.