Couple of hints for leveling. You were wise to go to the Resource Usage view. Of course, it you only have a few hours over the standard work day here and there, ignore the overallocation. You can’t plan work to be precisely 8 hours anyway so a 9 hour day of work can probably be accomplished in the standard work day. If the work is more than 6 weeks in the future and there is only minor overallocatioin (a few days with 12 to 16 hours here and there) – ignore it. When you get to that point in time tasks will have ebbed and flowed and the overallocation probably won’t exist. You will want to look at your possible overallocation every time you do a schedule update. Save your file before leveling – sometimes you will go out to 2049 and the undo may not get you back to where you were. If you use the Level Resources feature, use it one resource at a time. Go to the Resource Sheet and highlight the resource to level. I also suggest week by week leveling. If you have 16 hours one day and zero hours the next, of course you’ll split the work beteen the 2 days. Anyway, if you have highlighted one resource and go to Level Resources, the tool will ask if you want to level all resources are the selected ones. Choose selected ones and do the leveling. Then go back to the Resource Usage sheet and look again for overallocations. Level a second resource if necessary.
The problem with leveling all resources is that if there is one hour overallocated for any resource, the tool will rearrange tasks for that one hour. By looking at the resource usage, you can catch those cases yourself. You can also set the tool to level only if the task exceeds 9 hours (or 10). That way you and ignore days where (2) 4 hour tasks and a one hour tasks imply the work cannot get done that day – it usually can.