Sure, I'd be glad to assist with your upcoming trip to Poland, specifically to the cities of Warsaw, Radom, and Plock. Here are some key tips you may find helpful:

Best Time to Visit:
The best time to visit Poland, in order to enjoy mild weather and limited rain, is between May and September. The summer months of July and August are generally the warmest, but they're also the busiest, so you might want to consider the shoulder months of May, June, or September for your travel.

Route and Accessibility:
Warsaw's Chopin Airport is well connected to many international airports. After landing, you can take public transportation or a taxi to the city center. To travel between Warsaw, Radom, and Plock, consider using intercity trains or buses which are quite efficient and affordable.

Accommodation and Booking:
There are plenty of accommodation options available in Warsaw, Radom, and Plock, from high-end hotels to budget-friendly hostels. Airbnb is also quite popular. It's recommended to book your accommodation well in advance to secure the most competitive prices and availability, especially in peak season.

Clothing and Essentials:
Summers are generally warm, so light clothing, a hat, and sunscreen are musts. However, do pack some light layers for cool evenings. If you plan on visiting churches or other religious sites, having a scarf or shawl for covering shoulders might be useful. Don't forget a good pair of comfortable walking shoes too.

Health and Safety:
Poland is a safe country for tourists, but standard precautions apply. Always keep an eye on your belongings, especially in crowded places. Tap water is perfectly safe to drink. Standard vaccinations including measles, influenza, and diphtheria are recommended.

Local Etiquette and Respect:
Poles are generally formal and polite. It is customary to greet with a handshake. When visiting churches, maintain a respectful demeanor and dress appropriately. Remember to say 'Dzień dobry' (Good day) and 'Dziękuję' (Thank you).