One of your most precious assets as a Captain is your mental capacity. Try to glean information about what capacity is and learn some methods to preserve or even increase it.
Here are some tips:
1. Don’t try to do everyone’s job. Delegate and trust people to do their jobs correctly. Support and verify as required. Having said that, it’s important for people to be sure about what it is you want them to do!
2. Learn to identify time-critical points in the pre-departure process and make an effort to respect them.
3. Inevitably, problems will arise which will require your input and decisions. Keep the rest of the show on the road by delegating “normal ops” to the F/O, Cabin Crew, Engineering, Dispatcher, etc. and then get stuck in to the problem.
4. One way to increase capacity is to be able to do most normal operations and SOPs without too much mental effort. The key to this is familiarity and confidence. Practise as much as you can, on the line and in the sim.
5. As others have said, be very familiar with the layout of the company manuals and know where to find stuff quickly. You will need a clear working knowledge of the Fuel Policy (planning and in-flight), the MEL/DDG, Low-Vis Ops, and the FTL scheme.
More generally:
6. Ask your skippers for permission to act as the PIC (as constrained by your manuals) and then ask for constructive feedback afterwards. Engage them in some “what if?” discussions as appropriate.
7. Ask cabin-crew, dispatchers and other co-pilots what they see as “good Captain’s behaviours” and try to emulate them.
8. Don’t be afraid to ask for help from any or all of your resources, in the pursuit of good CRM.
9. Make the best decisions you can with the information that you have at the time. Be prepared to change your decision if new information comes to light. Be aware that you may need to justify that decision later.
10. What is a “best decision”? That which optimises safety, compliance with regulations, and company commercial interests, IN THAT ORDER.
11. Try always to have a plan B and maybe even a plan C in your back pocket, particularly when planning an arrival into bad weather. Set time and/or fuel limits for making decisions regarding holding at destination, diversion, etc. Make sure your colleagues are part of this process.