Space Marine chapters are the most common article on this wiki, and on various forums, image boards, etc. that host 40k content. Thus, due to the number of Chapters, the general quality is lacking. People often have their chapters fall into a variety of basic cringe worthy tropes or themes, which this guide will attempt to identify. Furthermore, it will look into other common issues and attempt to advise you on how to fix such problems.
The Inquisition and the High Lords of Terra
Space Marine chapters on the wiki often fall into the incredibly common trope of "hating" or "disliking" the Inquisition or High Lords of Terra based upon the idea that such organisations are corrupt, evil, etc, and often defy their authority or position.
This is one of the few tropes that can possibly work with good explanation. The High Lords of Terra are nearly as incompetent as some would like to depict them, and the Space Marines would need a incredibly good reason to have opposition for those second only to the Emperor of Mankind. Attempts to disobey or oppose the High Lords of Terra often end badly, even with the best intentions.
The Inquisition likewise is not nearly as incompetent as some would like to depict them. It is not a formal organisation, more a vast web of individuals and bands of people working together, meaning that individual personalities and beliefs influence their decisions. Thus having a Space Marine chapter "hate or dislike" the entire Inquisition makes no real sense. Furthermore, Inquisitors have limited power over Space Marine chapters unless granted it's actually within their jurisdiction.
Grey Knights are also an issue. The Grey Knights are part of the Ordo Malleus (one of the three Ordo's of the Inquisition), specialized in the role of Daemon hunting. Your Space Marine chapter - unless it is summoning Daemons - will doubtfully have issues with the Grey Knights, and Space Marines are subject to mind wipes after encounters with the Grey Knights. Very few Space Marines know of the Grey Knights, and those that do probably do not know of their true purpose. Chapters investigated for Daemonic taint would be receiving visits from the Ordo Hereticus, whom deal with internal threats of Heresy.
A special canon example of this; the Space Wolves had a spat with segments of the Inquisition and the Grey Knights over Imperial Guardsmen and Citizens after the War of Armageddon. Since exposure to Daemons is almost certainly a pathway to corruption for normal humans as well as all manner of unpleasant things, the Inquisition agents there present moved to liquidate them. Angered by this, the Space Wolves decided to defend the brave Imperial Guardsmen (who would almost certainly become future servants of Chaos), fighting both the Grey Knights and Inquisition. This almost caused the Space Wolves (a first founding chapter) to be declared heretics.
The Codex Astartes and Organisation
Space Marine Chapters generally follow the Codex Astartes, a set of guidelines and rules which was implemented by Roboute Guillman after the Horus Heresy. They limit Space Marine forces to a thousand men (including reserves) and pushed the Space Marines from general armies to special operations forces and shock troops. It is a rare occasion when an entire Space Marine chapter deploys. Some Chapters, like the Black Templars and the Space Wolves, do not follow this and have their own organisation, both possessing notable numbers.
Chapters over a 1000 men must have admin permission (and, of course an accompanying reason). Chapters with large numbers (even the most loyal or fanatical) are often under suspicion of heresy. If another heresy broke out, the divided Space Marine chapters would not be able to be so easily drawn into one side, though their lineage would almost certainly have an influence. You will never have a Legion. Ever. The resources simply don't exist.
Some Chapters on the wiki have adopted their own codex, often with their own special ranks and names. Of course this will cause conflict with codex adherent Chapters.
Space Marine chapters aren't always friends. Chapter Rivalries exist on ideological basis and beliefs, and can lead to all sorts of issues. All out rare is relatively rare, and it is mostly limited to skirmishes and so on. We'll take the ever so popular Ultramarines for example.
The very common "Chapter Rivalry" on the Wikia is the Ultramarine Chapter. The Ultramarines have been a source of upset for an incredibly long time. Ranging from people reading this or this. Of course if you took this seriously, we have a place for you. Otherwise, keep reading.
"Sticking it to the Ultramarines" has always been a very common troupe on the wikia, much like people having their chapters opposed to the Inquisition and High Lords. You really would really need a very good reason for the Ultramarines and your own chapter at odds. Simply doing to it to "hate what's popular" or to "be against the norm" (which has become incredibly common) isn't intelligent nor is it original. Furthermore your chapter will probably be at odds with the Ultramarines allies, and their successors.
There are legitimate reasons for your Chapter to hate or dislike another in the context of the universe, and not just because you simply dislike said chapter. Good canon examples are the Marines Malevolent and the Salamanders, the Flesh Tearers and the Salamanders, the Minotaur's and the Salamanders, etc.
Xenos are people too and the good guy Chapter
The trend of making Space Marines out to be noble heroes who are kind or benevolent to innocents in the Warhammer 40,000 universe, to the point where they are "laid back" with Guardsmen or other general soldiers and go out of their way to not cause civilian causalities. This often seems to find basis in the Salamanders, or general opposition to the Warhammer 40,000 universe's theme of unpleasantness.
This troupe is incredibly overused, and does oppose the general theme of the Warhammer universe. Space Marines as post-human super soldiers with very little humanity who where at best a temporary solution to the issue of reclaiming the galaxy. Why exactly does your chapter care for innocents? (Being Innocent Proves Nothing). The Warhammer Galaxy sees death on such an incredible scale, and Space Marines are trained to be emotionally stunted to the horrors of the universe. There are Space Marine chapters who are incredibly brutal because of this.
Thus, a string of Chapters exist that hate the High Lords of Terra, the Inquisition, etc, because of this "Good Guy/Rebel syndrome" against the leadership or the norm. It's unfitting.
Likewise, the trope of special alien friends has also worked it's way into the wikia. Space Marines are trained to fight and kill Xenos. Alliances are rare and strained, and don't last long. There is no reason to have these marked out, and draw attention from the Ordo Xenos and other chapters. It's mostly alliances with the Eldar, and most of the Imperium can't even tell apart the distinct Eldar cultures, while the Eldar's reputation as manipulative, cunning, greedy, exploitive, feeble and as degenerates is common in the Imperium. The Tau are slightly different, but alliances with any xenos aren't long lasting or respected.
The Chapter Character and the Not-Primarch
Another common issue is the Chapters "main character" - often a Chapter Master or Captain - whom the fluff (mainly the history) of the Chapter is focused upon. This means that the actual character of the chapter is diluted is often left to but a few distinct paragraphs, which is common with Games Workshops Special Characters. Try to avoid this, though intertwining character and chapter is fine.
The Not-Primarch is the Chapter Character who is the long term leader (often as old or older than Dante, the oldest living non-Dreadnought Space Marine) who is effectively it's spiritual leader. Space Marines can die of age. They are not immortal, and in the 41st Millennium, living a long life as a Space Marine requires some skill. Not-Primarch's might even be referred to as Spiritual Primarch's, instead of the actual gene-lineage.
Avoiding all of these things is almost certainly a good course of action.