If you weren’t aware, OSHA is in the process  of establishing a ‘new’ rule (could be years) for confined spaces in construction (here).
In the meantime, if you plan on entering a space that is confined, below is my “standard” answer: Get help!
What I mean by this is; obtain some assistance as early as you can. Ideally this might even be before you bid the job. I often suggest to  send a superintendent or project manager to a 1/2 day training. Do not rely on the owner, or your general contractor to “safely approve” your employees entering this space. It is your job!
Although confined spaces are simple by definition (restricted opening, large enough to be in, and not meant to be occupied) , they can get  complicated easily. The first thing to consider is what is/was in the space. Secondly, what are you bringing into it? If those two questions are answered completely, the dangers are usually identified.
When reviewing, consider: electrical, oxygen, engulfment, entrapment, access (ingress & egress), coatings, noise, slips, temperature and emergency response (this is NOT an exhaustive list).
There are many other items and steps to have a well-run confined space program. Take a class, know the space, and train your employees. There are many resources at Federal OSHA and at your state OSHA, like Washington here, or like this one from Oregon.
