Commscope makes a range of prep tools that have good productivity but are quite expensive for the hobbyist.
There are different forms of connectors for LDF4-50A, this article discusses a modern type that uses a collet to clamp the cable to the connector body.
There are many ways to prepare the shield end. This article describes one using a fine tooth pull saw which makes for good results for a novice.
Above, an Excel thin kerf razor saw #55001 which has a K5 handle and 30490 46tpi pull saw (~$20 on eBay).
Above, a 3.6mm (0.14″) zip tie is pulled quite firmly into the valley of the corrugated shield to serve as a saw guide. Note the partial cut. The width of the zip tie is critical, and this width is common. The objective is to trim the shield just a little towards the end from the middle of the crest. (Normally you might have the jacket trimmed further back to accommodate the o ring and back of the connector, but it can be trimmed when the cut is complete.)
You could buy an expensive gauge tool for this, but if you are doing only a few connectors, the zip tie works well. Zip it up firmly and cut about 60° around the shield without cutting deep into the dielectric, slide the zip tie around and continue the cut. Rotate the zip tie so that the new cut is from uncut into the existing cut which guides the saw.
Above is the trimmed shield with most of the dielectric removed. I like to leave some dielectric at this point to protect the inner conductor during flaring of the shield.
Above, the collet has been slid on and locked into the first valley and then the shield progressively flared. Note that this type of collect is almost impossible to pull back off, make sure the jacket is trimmed properly, O ring greased and in the correct valley before pushing the collet onto the cable.
Blow any copper shards from the work as you work to avoid them becoming embedded in the dielectric.
For this demonstration I have used a short piece of cable with the jacket stripped so I could get the collet off by pushing it to the other end. Above is a pic that shows the extent of the flare, it is not great but it is essential to proper performance of the connector. When the inner conductor is cleaned, cut to length and dressed the connector can be assembled and the collet nut will force the against the cone in the body and should be done up quite tight to properly clamp the shield for a reliable low resistance, low IMD connection.
I apply silicone grease to the collet nut threads and O ring, the O ring from collet nut to shield, and a very thin smear to the prepared centre conductor.