Last night in my small group one of the players caught me in an error in my storyline, nothing major that couldn't be easily fixed for continuity, but on something that I in retrospect should have noted. As a DM, I generally plan out a generic plan of what I want to occur, more of a point A and a point B and how the players choose to get from A to B is up to them and I tend to improvise in between. Unfortunately this means that I may miss out on some details along the way in my notes.
The party has returned to the town they were supposed to assist with no assistance and a level of uncertainty of innocence in regards to the death of the kind they were sent to get assistance from. There were 3 groups that are suspected now, the party, a dwarf who had met with the King prior to the party, and a group of women who were there to see the King afterward. Unfortunately, I forgot about the group of women last night since they weren't in my notes. While this was retconned, I still looked a bit silly for forgetting a group that one of the party members believed to be the culprits.
Ultimately, this isn't a major issue because it is just as simple to do a minor re-explanation to correct yourself and move on. This does, however, bring up a great thing to remember when you have the style of improvisation DM'ing like I do, and that is to document what happens. I have a small journal that I write down what happened in what session and what date it happened so when I plan sessions I can go back and see what had happened to tie everything together, but when I miss details it could take an otherwise sewn up conclusion to the story and create some doubt. While it isn't a difficult thing to do, I make sure that I have either a notebook, journal, or computer nearby to make some notes of what happened during a session and what the plan is for the party in the next session so I can come up with an idea of what I want to plan for the next session.
Documenting your adventure helps as a DM, but also serves as a bit of nostalgia too when you can look back months and see where the party was to what they have become now. There really is no reason to not document your adventure, and it really can help add that extra layer of cohesion to your homemade campaigns. You as a DM will notice the difference, and if this is something you have had issues with, your players will notice and appreciate it as well.