Hello! That's exciting, you've chosen some great places in Peru to visit. Let's outline the key points for your trip.

Best Time to Visit:
The best time to visit Lima is from December to April, it's summer and the weather is pleasant. As for Trujillo and Cajamarca, they have a fairly mild climate all year round.

Route and Accessibility:
You can arrive at Lima through Jorge Chavez International Airport which has connections worldwide. From Lima, you can take domestic flights or buses to reach Trujillo and Cajamarca.

Accommodation and Booking:
There are plenty of accommodations available in all three cities, ranging from budget to luxury hotels. It's recommended to book your accommodation in advance, especially during the peak season.

Clothing and Essentials:
For Lima and Trujillo, light summer clothing, sunblock, sunglasses, and a hat are essential. For Cajamarca, pack layers as temperatures can vary. Be sure to bring some warmer clothing for the cool evenings.

Health and Safety:
Drink bottled water and avoid eating street food if your stomach is not used to it. Public areas are generally safe but use common sense, especially at night. It's recommended to have travel insurance.

Local Etiquette and Respect:
Peruvians are warm and welcoming. Respect the local customs and traditions. When visiting religious or historical sites, behave appropriately. It's good to learn a few phrases in Spanish as it is the primary language.