I suggest to all first-time computer-assemblers that they have a 'coach' along with them. Someone who's built many, because there are so many shortcuts and "best ways" to assemble the parts - first things first, second, third.
For example... every motherboard comes with a small metallic 'shield' that fits in the case, where the motherboard's built-in port connectors (Mouse, Keyboard, USBs, Video, speakers, etc) fit. That little shield needs to be in the case, first.
The standoffs in the case need to be inserted first.
These are small issues and, if I put in the motherboard too early, I can fairly easily pull it out and install all the First Parts 'first'. But having a coach, an experienced assembler, helps sooo much. Assembly may only take 30 minutes, maybe less, maybe a bit more.
Having an experienced friend will make sure the best, quickest ways are known.