For all the info you will ever need to watch any preseason NBA game, whether it be on your television or through a streaming device, continue below. This entry is broken down into: TV viewing options and online streaming options, to make it easy.
TV Viewing Options
NBA TV, TNT, ESPN
NBA Preseason Basketball Schedule, TV & Live Streams (with available ticket info for all games as well)
As you can see from the above link, most every NBA preseason game will air exclusively on the NBA TV channel. Check with your cable/satellite provider to see if you get the channel. Keep in mind most basic cable packages won't offer the channel in their bundle initially, so it will likely be an extra charge. Likely reasonable cost though.
To see what channel your provider airs NBA TV, or to see if your provider offers it, use NBA TV Providers list.
TNT and ESPN will also be airing a few preseason games as well. Again, use the NBA Preseason TV schedule above to see which games air where.
Online Streaming Options
NBA League Pass, SlingTV, Playstation Vue, Watch TNT, Watch ESPN
If you have a cable TV package, WatchTNT and WatchESPN will be live streaming a few preseason games, and you can access them on your mobile device, PC or Mac by going to their respective sites, and using your cable login info for live game streaming.
If you don't have a traditional cable TV package, consider SlingTV or Playstation Vue. Both are internet cable package alternative options that include TNT, ESPN and most importantly NBA TV. Both also come with a free trial period. SlingTV is more affordable, but Vue is possibly more convenient for PS3 or PS4 users.
And for the ultimate NBA preseason viewing option:
NBA League Pass is the best place to watch any NBA preseason game, but it's far from the cheapest.
Full access will run you $199.99/yr. Or $249.99/yr for commercial free. If you wish to go monthly it's $28.99 or $39.99/month respectively.
It's a little better than it sounds, as this actually gives you access to all the regular season NBA games as well (that aren't already nationally airing in your area). And their on demand feature makes all games available to watch in full, just 3 hours after any game airs. And for those just looking to follow one particular team, they offer a discounted $119.99/yr rate (or $17.99/month).
On top of that, you also get NBA League Pass Audio, so you can listen to all NBA games live. And if you just want the radio option, that is far cheaper as a stand alone service; something I would highly recommend for just a one time fee of $9.99/yr.
Hope this helps. Enjoy the NBA preseason!