Don't you just hate spending hours and hours in the garden only to get ugly, cracked and split fruits?
This is a symptom of inconsistent soil moisture. Some plants benefit from soil that dries completely between watering, but tomatoes are not among them.
Tip #1 is to water daily. Don't water until the soil is sloppy wet, but try to maintain a consistent moist soil at the root zone.
Tip #2 is to bury your tomato plant as deep as you can, even if only a couple of leaves remain above the ground.
I start my seeds in plug trays, then transfer those into 4" cells, then into 1 gallon containers after stripping off limbs and leaves, burying as much of the plant as the container will allow. Then I grow the plant tall and lanky. When it comes time to transplant into the garden, I strip off all but a few leaves at the very top and bury the root ball and the main stem. Some of my tomato plants were buried up to 3 feet deep!
Any buried stem is going to send out roots. A big, hearty root zone will make for a strong and prolific plant. Getting the root zone extra deep goes a long way to maintaining enough moisture to prevent your fruits from cracking and splitting.
The cracked fruit above was grown in this bag. I often forget to water these two plants more than once or twice per week. They do get some moisture from the soaker hose below the bag, but just enough to keep the plants alive.
Happy gardening!