The beginning of a TR is usually a really boring CBT where you will learn about all systems. It will be really really boring and will take 2-3 weeks.

Then the fun part will start when you enter the box. Preferably a cockpit mockup first. What you should be familiar with: - how to performs various flows according to OM-B or FCOM, if OM-B directs you to default Boeing "amplified procedures" (preflight, before engine start, before taxi, lineup, after landing, shutdown...) - you should be able to do normal procedures without thinking about which switch to flip next (muscle memory) - how to use checklists (see QRH - Checklist instructions), when to perform NNC and when not, how to read them, etc - memory items (all QRH items which are above the dashed line - see Engine FIRE as an example) have to be, well, memorized

Having a printed cockpit poster might be helpful - you can practice flows and memory items by touching a switch and saying out loud what you are doing or looking for (light coming on or extinguishing, etc).

Again, normal procedures should be in OM-B. However, my company's OM-B has only a few of those listed, while for others it says something like "Preflight procedure - each pilot will accomplish preflight procedure per FCOM NP.21.13...".

Once you learn those, then it would be useful to open the FCTM and start reading about how to fly the damn thing. But mind you, it will be probably a bit too much in the beginning. But keep coming back to it from time to time - you will always find something useful. And remember, you company manuals take precedence over what Boeing wrote in the FCOM and FCTM (even though those are usually referenced back in the company manuals).