It's common for a hardwood floor to transition into one made of tile. It can happen in the doorway between the living room and the kitchen, for example, or near the fireplace. If the floors are at different levels, you need a transition strip in order to avoid creating a tripping hazard. You can buy preformed strips or make one yourself. If the floors are at the same level, however, you can often dispense with the strip because the tile grout makes an effective transition all by itself.
Design the hardwood floor so that the boards adjacent to the tile floor are running lengthwise with respect to it, if possible. If the tongues of the boards adjacent to the tile are facing the tile, cut them off with a table saw. Top-nail the last boards with 2-inch finish nails and sink the heads of the nails with a nail punch.
Draw a line the width of one flooring board away from the edge of the ungrouted tiles with a straight edge and a pencil, if the flooring runs perpendicular to the tiles. Lay one course of flooring boards on the tile-side of the line to act as a border for the hardwood. Cut the tongues off of these boards and lay them so their grooves face the hardwood floor. Top-nail them and sink the heads with a nail punch. Finally, lay the rest of the hardwood floor so that the tongue ends fit into the groove of the border.
Lay the tiles so that the gap between the tiles and the hardwood is the same as that between all the tiles. When you grout the tiles, treat the gap in the same way as all the gaps between the tiles, and fill it with grout.
Measure the difference in thickness between the hardwood and the tile. If there is a difference, purchase bevelled transition strips made of the same hardwood as the floor, so that they will be flush with the higher surface when you attach them to the lower one. If your flooring dealer doesn't have transition strips of the right size, you can make your own.
Set the fence of the table saw about 1/4 inch from the blade, then set the blade angle so the distance from the top of the fence to the inside edge of the blade is the same as the difference in thickness of the flooring materials. Run spare flooring boards through the blade to make bevelled transition strips of the correct size. Sand and finish your homemade transition strips before you install them.
Spread tile adhesive on the backs of the transition strips, set them in place, and place weights on them to hold them down while the adhesive dries.
If the tile and hardwood are the same thickness, you probably don't need a transition strip. If you prefer to have one, you can buy hardwood or metal strips to hide the transition.
Always wear safety glasses when using a table saw, and use a push-stick to push wood through the blade, especially when you are cutting bevels. When you have pushed a board completely through the blade, turn off the saw and wait for the blade to stop spinning before reaching for it.