If you are not using a Rekenrek in your classroom you NEED to go and purchase one or make one ASAP. It is such an excellent tool when it comes to building number sense and fact fluency with your students.
Currently, my students are working on their understanding of the "one more" and "one less" relationship. I would show a number of beads on my wooden Rekenrek that my students would then quickly report back to me. I would then slowly slide another bead over saying "one more is..." and the students would report the new number. We did this as a warm up fluency for a number of days. When they were quite automatic, I was ready to link this understanding to the equations. On whiteboards, students would write equations related to what they saw and counted on the Rekenrek.
When the students were quite proficient with this skill, I moved this practice over to their math centers for mastery. I created this "Rekenrek board" out of a page protector, pipe cleaner and a few beads so that my students could practice this skill on their own. I can easily slip in a page with number bonds, addition equations, missing parts, etc. and they can use the Rekenrek tool to help them visualize the results.
This is NOT about finding a procedure for adding or subtracting one. This is about giving a visual cue to understand what it means to add or subtract one. As they are working on their centers, I am quick to check in with the student who is "playing" this game and I push them and ask questions which will allow them to internalize the skill as they demonstrate proficiency. These are questions like "You built 7, can you think about what one more will be without even pushing over another bead?" or "Look at your next problem, can you picture what 5 might look like in your head? Think about what one more will look like. What is 5 + 1? Now, build it with beads to check your thinking".
After my students were quickly able to answer these facts I made what may be considered a controversial move. I put the facts onto flash cards. GASP! But hear me out here. How many times have your students learned a new skill and then over generalized that skill to #AllTheNumbers!!! I know this will be a problem so I have just decided to be proactive about it. Each time my students learn a new set of facts I write them onto flashcards in a colored Sharpie marker. All of their +1 facts are on flashcards written in blue marker. My students also know their 0+ and +0 facts as well as their 10+ facts. The 0 facts are all written in a magenta marker and the 10+ facts are written in green marker. My students have one math center they can go to where they can individually or "race" a friend to practice their facts. My sole purpose in doing that activity is for them to realize that their new understanding about how to "think one more" can NOT be applied to all equations. Just the +1 equations. When they go through the flashcards and see the different colors their brain is triggered that this is a different type of fact and they need to change their thinking. I have had MINIMAL over generalization errors since employing this technique. Not to mention that my students feel SUPER successful when going through a stack of facts that they know. They love it. And I love that they know 30 of their addition facts without "memorizing" a thing.