I live in south central Texas. In late winter I prune off all of the existing fronds. If it has a developing flower, I do not prune off any of the fronds. I let the flower to its thing, go to seed, then I prune off all fronds and pull all of the seeds out.
Make sure you throw them in the garbage if you have dogs. Eating just one of the seeds will almost always kill them. Cats are generally not attracted to the seeds, but dogs are.
Mine have always set off a new group of fronds, and they are beautiful. Doing this also helps the sago grow taller. My neighbor has one that has a 5-foot trunk, which is about 18 years old. The way I prune it is to grab the frond mid way up from the base, pull it down sharply, and it will almost always snap off pretty close to the base. After you've snapped them all off (or some), you can use pruning shears to make them a bit neater. I've been growing mine for 11 years. When I moved into my home, I found it buried in the backyard in the shade, so I transplanted it to the front yard. I have never fertilized it, nor have I ever had any problems with it.
I transplanted a smaller one I had to my aunts yard in Houston. She never prunes hers, except for the pups. The spread is much larger than mine, the trunk is only about 1 foot, and it's 7 years old, and the two bottom sets of fronds are touching the ground. Long-winded, but I hope this helps.