Sure, I would be happy to! Embarking on a trip to Athens, Sparta, and Metéora will be a rewarding experience. Here are my travel tips to make the journey unforgettable:
Best Time to Visit:
The best time to visit these places would be during the shoulder seasons:
April-May and September-October when the weather is favorable and tourist crowds are moderate.

Route and Accessibility:
Athens is widely accessible by air, it is linked to all major cities worldwide. Sparta is about 3 hours drive from Athens. Metéora, on the contrary, is a 5-hour train ride from Athens.

Altitude and Acclimatization:
The altitude of these places is not significantly high. Acclimatization won't be much of an issue. However, do stay hydrated and give yourself some time to rest after the journey.

Accommodation and Booking:
Athens and Metéora have a range of accommodations from budget to luxury, cater to every traveler. While, for a stay in Sparta, you might have to settle with mid-range and budget stays. It's best to book ahead of time especially during the peak season.

Clothing and Essentials:
Casual, comfortable clothing will work in these places. Do not forget your sunscreen, hats, and sunglasses to protect you from the Mediterranean sun. In Sparta, you might want to pack some sturdy walking shoes.

Health and Safety:
Always remember to keep your belongings secure, as pickpocketing can occur. Keep emergency numbers and information handy.

Local Etiquette and Respect:
Greeks are warm and hospitable. Respecting local traditions, customs and following dress codes in religious places will be appreciated. Be polite while haggling in local markets.

Enjoy the spectacular archaeological sites in Athens and Sparta, and view at the splendid monasteries in Metéora!