Honestly the more you fly the easier it’ll become.
Preparation and organization are key. After you plan/file the flight, look it over thoroughly and brief it to yourself. Go over every segment of the flight from start to finish (weight and balance, weather, speeds and altitudes, frequencies, airport information / taxi charts, departure constraints, arrival and approach constraints, alternates, missed approach procedures etc.). Make sure you have everything you need ready and accessible before the flight begins. If you get sidetracked or confused and are in a critical stage of flight like climb or descent then you will get overwhelmed. So then dont get sidetracked or confused - be a step AHEAD of the aircraft at all times, have your charts ready, be organized.
It’s smart to rebrief (this goes under preparatation). People forget things, and thats totally normal. In addition to briefing the flight before I hop on the sim, I will also brief critical items in flight BEFORE they happen. This is usually quick (bec one can recall most of the information from the pre-departure briefing).
An example is the descent phase; during cruise, as the aircraft is nearing top of descent, I’ll check destination weather, plug in landing wx and landing perf info into the FMC/MCDU, and I’ll pull out the STAR and the Approach plate. I’ll give them a thorough look over, I will rebrief the descent, and will “put” the charts somewhere visible so that I can reference them. That’s it. That’s all you have to do. You are now prepared for the descent because you were proactive. If you are reactionary and not proactive. Then you will absolutely fall behind the aircraft, and it will drag you along the timetable until you land.
If you are prepared and organized, a flight should feel like less of a struggle and more of a sequence. Less like a sprint, more like a jog. Less like drinking water through a firehose, more like taking small sips. Then at the end you’ll feel satisfied and not like you were just curbstomped.
If you’re having FMS or other aircraft systems troubles, then that goes under preparation. Watch some youtube videos on it and practice it a bit and you’ll manage. It’ll be less of a chore and more of a saving grace. Like other systems, FMS/MCDU gets demystified really quickly if you set aside your worries and just devote some time to proficiency. After some repetition, it wont take much brain power to operate at all. Which then opens the door to being able to operate it on the fly quickly without any trouble at all. Stick with it, you’ll be alright.
I should probably include that I am NOT an airline pilot. I simply try to emulate real world airline workflows as best as I can because that’s what works.