I do a very similar process as reinbeau, where I cut the pieces up very small (if it's not already ground) and put it into my soapmaking crock pot on low. It takes a while, but eventually it all melts and I let it cook on low for a few hours (not letting it boil) until as much fat as possible has melted away from the sinew-y bits. Then I strain it through a coffee filter and let it sit on the counter until it hardens up, and then move it into the refrigerator.
The first time I rendered beef fat the butcher had taken a whole bunch of scraps and put them into the grinder, which certainly made the process easier, but there were quite a few beef bits that needed to be strained out at the end. The second time I did it I specifically ordered the fat from around the kidneys (aka leaf fat, I believe), and it arrived in big chunks but did not have meat bits attached and I feel it made for better soap. The tallow was less smelly, too.
I tried wet rendering once but didn't care for it.