Many boats already have all the deck gear necessary to fly a gennaker. If not, setting up your boat to sail a gennaker is usually a fairly simple.

Halyard
The ideal situation is to have two separate halyards one for the headsail(s) and one for the gennaker/spinnaker.

If you have only one halyard only one sail can be used at a time. This presents a problem especially if you have a roller furling system installed. I would suggest adding an additional halyard to keep things simple. The best location for the spinnaker/gennaker halyard installation is above the headstay attachment on the mast. This location minimizes the possibilities of chafe no matter which direction the sail pulls from. The halyard can be lead internally into the mast via a sheave or the halyard can be set up externally with a block (smaller boats only).

Tack Line (two different options are available):

The tack line can be dead-ended at the bow.
The tack line can come directly from the tack of the sail and cleat on a fitting on the forward foredeck. Ideally the tack fitting should be forward of the headstay. For example a bow cleat or the bar that holds the anchor stem into the roller are usually good enough.

The tack line can be adjusted from the cockpit
The tack line can come from the sail to a block (snatch blocks are ideal but expensive) on the bow then lead aft to the cockpit. You may need to run the tack line through a fairlead every 5' or where needed to keep the foredeck clean. This gives you added control to adjust the luff tension of the sail.

Make sure whatever style fittings and line you use can carry the load the sail requires.

Turning Blocks
After the sheets have been attached to the sail they should be lead aft to a turning block located near the stern of your boat. From there, each sheet is led forward to a winch. Spinnaker winches are great to have, but if you don't, your regular headsail winches will do the job. Your turning blocks must be attached to a sturdy deck fitting. If you don't have a toe rail that will work for this purpose, install a pad eye or other strong hardware with a backing plate.