It appears you have already done at least the first level of planning, and are now interested in what you might do over the next few days. At this stage, I would have a general stage plan, including an idea where I will take rest days. I will also have made a provision in my overall plan for a reserve day or two in case of illness or injury, and to have a couple of days in SDC at the end.
In planning the next few days, I start with the current outline stage plan. This might have been revised from my original plan if I have walked more or less on some previous stages, so where I am might be different from my original plan. From there, I do a quick calculation of where I might want to stay for the next few nights that are a reasonable match with the daily distance that I think I will be comfortable doing. There won't be a perfect match, so there will be some options that might be a bit of a stretch, and others that might be a bit short if I am going to stay broadly within the overall time that I have available.
At this point, my approach has varied a bit depending on whether I am booking ahead or walking with as few reservations as possible.
- If I am doing stages much longer than my target daily distance, I prefer to have a place reserved where I want to stay, and if that isn't going to be possible, then I will look for an option with shorter stages.
- If I am walking without too many reservations, I will check what accommodation options are available around where I plan to stop each day. If there are only private accommodation options such as hostels and tabernas or the like, then I will make a reservation a day or two ahead.
At this stage, I will check how this fits back into my overall plan. This is rarely a distinct process, more something that is going to in the background while considering the options for the next few days. I don't worry too much if it looks like I might arrive a day early because I might do a series of slightly longer stages, but provided I am not going to be more than a day later in SDC, I won't worry too much provided I can change any accommodation bookings there.
I normally only make arrangements for travel from SDC when I am in the last week or so. I can do this as I normally plan to spend a few days in the UK with family and friends following my camino before my flight back to Australia. This gives me a useful buffer, and I use this to avoid having to push myself to get into SDC in time to make a flight that I might have booked some months beforehand.
My final observation is that for my most recent caminos, I have planned to be within 10-12 km of SDC on the last night. I can then walk in at a comfortable pace, arriving at the cathedral in the early afternoon. I then attend mass the following day, and have a quiet day. If I still have another day, I might take a bus tour, eg to Muxia and Fisterra, or just visit some of the many places I have yet to explore in SDC.