1) Do not underestimate that first days climb over Napoleon route and I would recommend doing some kind of hill training. I learnt, after my third camino and Alto de Perdon, finally learnt the best way to walk up hills, small steps at a steady pace. Had I done that on the way up to Orisson I'd certainly look more attractive in the photos! Rather than a beetroot! It's really a steep climb, and I'm mid-thirties, I was so impressed and inspired by the 60-70 yo passing me by - they knew how to walk!
2) Blisters - I got many blisters on my first camino, thanks to too tight walking shoes (merrills) and using compeed, which really didn't help me. I learnt using looser fitting, good grip trainers resulted in no blisters and if you do get a blister use plasters.
3) Set your own pace - The pull of the "camino train" is an real unseen force - my walking pace is almost always set by the people up ahead of me, I never lose them unless I take a break! There are some days I'm thankful for that as it gives you energy and the inspiration to push on and other days when I really should not be allowing others to set my pace, like when the tendinitis is flaring. I have had a head cold twice on my last two caminos from pushing too hard early on. If your "limit" is 30k per day, start out with 20k days and build up, don't do 3-4 30k days out the blocks.
4) Put bags inside your morchilla (not plastic ones) - I have a cotton day bag I take around with me for after the days walk is over to attend mass or visit restaurants with pilgrim passport/money/snacks, basically everything apart from clothes and shower stuff and another bag to keep dirty washing separate. Nothing worse than not being able to wash your clothes and mixing dirty and clean clothes in your morchilla!
5) Shower Hooks - Many places have tiny shower areas with no hook or room to put anything, that cotton bag can hold your fresh clothes on a shower hook while you toss the old clothes you're wearing off and over the shower door. I am now highly skilled at getting dressed and showered in tiny spaces - much like wonder-woman! Not much worse than getting all your fresh clothes wet (sodden) before putting them on.
6) Energy to Walk - My body doesn't take well to energy in the form of a fatty chorizo or pie, it makes me feel lethargic on the walk, stock up on bananas, dried fruit and nuts for energy calories, plentiful and easy to transport and not smelly.
7) Snorers - They are inevitable. Bring foam earplugs (several pairs as you'll lose/wash them).
8) Listen to your feet/legs - If something hurts, try to readjust yourself, stop, rest, air out the feet, it's amazing how many times I've believed I was "done-in" to then be able to walk another 10k after an hours rest and chat with pilgrims. Especially towards the end of the camino, you just start doing higher average day kms, I remember sitting at some Albergues having called it a day, showered at 1pm after 25k and being quite bored and very able to do another 10k.
9) Remember why you went! - This may not be the case for everyone - but everytime I've been on camino there's been a question or some freshness needed to bring back to my spiritual life, some negativity has set in. Especially if you make friends and you're quite "tight", you can forget the purpose and just end up "having a laugh" - theres nothing wrong with that and maybe it's the medicine you needed in the end - but there were times I felt I should have been at mass or reading and I was drinking beer (lots of times!).
10) Don't just fall into the first Albergue you see when tired - Exhausted in Astorga, I really could not walk another step (or so I believed!) and fell into an Albergue I had read was not great. Well, cold shower, tiny thin bed, huge hot attic room, resulted in very little sleep.