Tack

Choosing the correct tack is essential. You need to decide whether you will ride Western or English. No matter which you choose, the next paragraphs apply to each.
Blankets:
When choosing blankets, or numnahs, you can use this simple test to see if the blanket/numnah is thick enough. You should be able to place your thumb on top and your middle finger on bottom, and you should be able to press and not feel the other finger. Your horse will have ensured comfort that way, and your horse will certainly not get saddle sore.
When choosing the saddle, choose what best fits you and your horse.
When choosing the bridle, choose a bridle with a gentle, true snaffle bit and with leather or nylon headstall. You can choose the reins, because you may have preferences. A hackamore is a bitless bridle. A horse that flings their head and does not respond well to a snaffle bit may not need a bigger bit, but rather a hackamore.
Choose a good halter. The best halters are hand-tied yacht rope ones, available at parelli.com and sometimes available on ebay.com. These rope halters prevent a horse from leaning on them, but can get a horse to yield easily.
As far as lead lines go, choose whatever. You may want something soft, to help prevent rope burn. You should use a 6 ft. line, because it allows distance between you and your horse.
Use common sense.