I decided to change my lower ball joints today because I noticed that the front driver side joint was squeaky. I can believe how bad the condition of this ball joint was. Is there anything I can do to prevent this from happening on my new ones?

 

New one didn't come with a boot?

 

Make sure to get greaseable joints. And yes, new one should have a boot.

 

Just leave the boots on, should last awhile.

You can inspect for water intrusion ever now and again with a squeeze. Water remains separated from the grease, with a squeeze it will come right out. If that's a the case, yea, should be replaced, it'll wear quickly once compromised. To check for slop, key to run to unlock the steering and while jacked. Move the wheel by hand and watch for slop. Stop mid turn and grab the ball joint rod and move it around if you can. It shouldn't move.

You can use an injection needle to refill with grease and help purge water. That will get them to last a little longer, but honestly, if the grease is diapering and they are holding water they should be replaced.

EDIT: - Added in this part after seeing screamineagles post above. If you use greasable. With greasable, you have to be careful not to over-grease and deform the boot.

That's about all, you can check for slop at the stops as well. By hand as explained and turning the wheel by hand outside the vehicle. No need to touch the steering wheel. Unless you have an assistant you can bark out orders too.

 

Are these the original? If so, 16 years is a good run for the boots.
Moog Problem Solver ball joints (the lowers) have smaller boots than OEM and others. They are also greaseable, so if you keep up with them, they should last at least as long.
What did you replace them with?