When planning a trip at high altitude, acclimatisation should be a priority (before time and money constraints) because when you take enough time to acclimatise, you lessen the risk of developing serious altitude sickness while increasing your performance and enjoyment in high altitude activities. So don’t forget that you are in Peru on holiday and that the point of it all is not to get ill but rather to have a great time!
It is important to take the acclimatisation gradually, increasing the altitude a little every day and making sure not to ascend too high too quickly. A common mistake is not to distinguish the difference between the various options for acclimatisation hikes. Simply because a hike is described as an “acclimatisation hike” does not mean that it is suitable to undertake on the first day that you arrive at altitude.
Being young and physically fit offers no protection. In fact it is young, fit people who often suffer the most from altitude sickness, simply because they tend to hike too fast during their first days of acclimatisation, a mistake that can be difficult to recuperate from, as once you have gone over your limit it can take days to get back to normal. It is therefore very important to take it easy, not overexert yourself and walk at a much slower pace than what you are accustomed to during the first days of acclimatisation.
Here are a few examples of suitable acclimatisation programs in preparation for a multi-day trek in the Huaraz region:

These are all great options that can be easily organised from Huaraz.
Please note that given that the day trip to the Pastoruri Glacier only includes one ½ hour of hiking on gently ascending and easy terrain, it is considered a much easier trip than the hikes to Lake 69 and Lake Churup, even if the altitude is greater. When talking about acclimatisation it is important to consider as much the final altitude reached as the effort needed to reach that altitude.
If you are planning to visit the ruins at Chavin de Huantar, it is of course advisable to do this trip first, as it does not include any hiking and only goes to higher altitudes briefly and by bus.
Please do not forget that if you suffer from jetlag or exhaustion from travel, it is wise to allow one day for complete rest before undertaking any activities.
And if you have spent time at high altitude during your trip, but during the week prior to your arrival in Huaraz you have been at sea level, all acclimatisation will be lost and you will have to start acclimatising again from scratch.