The most important is the idea what you want to build.
Then you should know your limitations (number of bricks, space, time,...).
For small(er) MOCs not much of a planing is needed. It is crucial to know building technics and as many as possible brick shapes from your head so you can realise your ideas without delays for searching for both.
For big(ger) MOCs a planing is wise approach. I do not use very sophisticated tools. Paper, pencil, ruller and calculator. I convert all dimensions in studs, draw a simple plan with measeurments in studs and start building. All details I do when got to particular section or when I am inspired with idea how to do it. Such approach is not good enough to start building and finalise in one goal. There is a lot of building, rebuilding, trying ... and have fun with it.
Yes, you could use LDraw or any other virtual tool and produce a plan to last stud. Then build it from real bricks, but I do not practise that at all. Never even tried. Like having a date on Net, or smell flower with gas mask on face.
Of course, virtual modeling can be usefull, if you do not posses certain bricks. You can verify your ideas and if you are satisfied purchase bricks and build real model.
If you are new to MOCs, try everything and see what suits you most. There is no 'one wisdom solves all enigmas'. Go and have fun with bricks. It it is not for you, go try another hobby. Only you can make yourself happy.