Mark the Tiles
Once chalking the lines and making the tick marks are done, set the tile in place to cut the sink opening. Align the straight-cut tile with the mark to make the L-cut for the sink. The only difference in the L-cut is that some materials are removed while leaving others. Make the marks on the tile where the sink opening is. Take the other full tile and align it next to the marked tile, and make the same marks on the tile. Make an "x" on the material that needs to be removed when cutting the tiles.
Note: On sinks that are self-rimming, remember the rim will "cover" the opening where the tile is, and it will later be set into silicone so it'll be sealed.