The best recommendation i can give is play on a corded connection not wifi.

But if thats not the issue then it probably comes down to computer specs, had a friend trying to play on a laptop that couldn't do anything because his pc couldn't handle the game.. sadly ffxiv has a lot more requirements then most other mmo's out there.
If you're able to consider upgrading your graphics card, get some more ram, and make sure your cpu is up to snuff, i know that is a lot of money and basically saying get a new computer, but sadly its the only thing that fixed it for me.