That's quite a big question. And its not an easy question (which is probably why you cant find many solid answers to it).
Dave has posted many videos about PCB design, so if you search the EEVBlog channel you can find a couple:
My best recommendation is to just go ahead and attempt to layout a PCB yourself, post it on the forum and get the feedback of other users. The best way to get good at PCB layout is to just practise.
Sure, there are some key rules that you should adhere to, such as:
- General layout and flow of components (connectors on side of board, power "section", digital "section")
- Grounding practises (Either star or planes depending on application)
- Isolation (HV, supply domains)
- Length/Impedance matching (more of an advanced topic, you probably wont find the need to do so)
- Minimise/Prevent dI/dt or dv/dt parasitic (current loops or parallel coupling)
- Good decoupling practices (moreso a schematic issue)
In terms of process? You can do that once you've drawn up the schematic in your CAD of choice (I'd recommend Altium, you can use KiCad or whatever pleases you), you can then lay out the PCB by placing components and routing traces/via.
Perhaps you could share the schematic/a first attempt and we could give you a pointer on where to get started?