Hello! It's great to hear that you're planning a trip to San Antonio, Dallas, and Amarillo in Texas, USA. Here are some travel tips for you.

Best Time to Visit:
The best time to visit these cities in Texas is during the spring (March-May) or fall (September-November). During these periods, temperatures are moderate and outdoor activities more enjoyable.

Route and Accessibility:
If you're traveling within the US, flying directly to San Antonio International Airport is the most convenient. For your trip from San Antonio to Dallas and then Amarillo, consider either renting a car or taking a domestic flight. There are also bus and train services connecting these cities.

Accommodation and Booking:
All three cities offer a wide range of accommodations, from luxury hotels to budget-friendly options. Booking through online platforms like Booking.com or Airbnb is convenient and allows you to compare prices. It's advisable to book in advance especially during peak season.

Clothing and Essentials:
For spring and fall, pack lightweight clothing with a few warmer items for cooler nights. Don't forget your sun protection like hats, sunglasses, and sunscreen. If planning to visit during summer, lightweight and breathable clothing is a must due to high temperatures.

Health and Safety:
You're advised to carry traveler's insurance for sudden health emergencies. In terms of safety, common sense precautions like not displaying valuable items and using safe transportation are recommended. Use bottled water if you're concerned about tap water quality.

Local Etiquette and Respect:
Texans are known for their hospitality. Simply being polite, respectful and adhering to common etiquettes will go a long way. Tipping is customary in restaurants, taxis, and services.