Hello! That sounds like an exciting trip. Here are some tips to make your journey to Berlin, Potsdam, and Brandenburg enjoyable and trouble-free.

Best Time to Visit:
The best time to visit these German cities is during the spring (April to June) or autumn (September to November) when the weather is pleasantly cool. However, Berlin is known for its incredible Christmas markets, so December could also be a magical time to visit.

Route and Accessibility:
Berlin, being the capital of Germany, is well connected by airline services from all major cities around the globe. Once in Berlin, both Potsdam and Brandenburg are well-accessible by public transportation such as regional trains, trams, and buses.

Accommodation and Booking:
There's a wide range of accommodations available in all three cities, from luxury hotels to budget hostels. It's recommended to book in advance especially during peak season. Websites like Booking.com and Airbnb can provide you with plentiful options based on your requirements.

Clothing and Essentials:
Depending on the time of your visit, pack warm layers for the colder months and lighter clothes during warmer months. Don’t forget a good pair of comfortable walking shoes as you'll be exploring a lot on foot. Carry a travel adapter for your electronics as Germany uses type F plug sockets.

Health and Safety:
Germany is generally safe for tourists. However, like anywhere, be aware of your surroundings, especially in crowded areas. EU citizens should carry a European Health Insurance Card (EHIC). Non-EU citizens are advised to have travel insurance that covers health.

Local Etiquette and Respect:
Germans are known for their punctuality and directness. Always be on time for any meeting or social occasion. When in public places, it's seen as respectful to keep noise to a minimum. Tipping around 10-15% at restaurants is customary.