I am Pluxus, 1d on DGS, 2d on IGS and moving forward. My goal is to reach 4d within the end of the year.
When stones on the 4th line are facing each other, as they do on the top, right and left side, then those sides are in general more urgent that when stones on 3rd and 4th line are facing each other as they do on bottom side. As a demonstration, playing at a would be a futile idea which holds little potential. As with all guidelines, there are exceptions, but unless you have a better plan, this is good to keep in mind. Depending on style, it is possible to prevent opponent's potential instead of creating for yourself, but even so, it should be done where it is the most efficient (at d for example).
Instead of a, moves like b, c, and d develop nicely and are all in areas of big potential.
If Black wants to overconcentrate White on the side, he can play the marked move. The standard variation is shown below:
The timing of and is crucial, if Black atari at first, then the peep at will lose its severity.
The idea is to make White invest many stones in the exchange, and if he has other stones on the side that makes him overconcentrated, then Black's plan is a success.
With the marked stone in place, Black can choose to connect below. White ends with a if possible. Before playing this variation, the position of the marked stone and the aji of the stone must be considered in a whole board perspective.
These 3 variations are only a small part of the possibilities and they should always be played according to a whole board strategy and never used blindly. If these variations cannot give you a satisfactory result then a different pattern should be chosen.