Sure, I'd be delighted to provide you with travel tips for your trip to Sri Lanka, covering Colombo, Jaffna, and Galle.

Best Time to Visit:
The best times to visit Colombo and the southern cities like Galle are from January to March when the weather is warm and dry. For the northern city of Jaffna, the ideal time is from February to mid-April or mid-July to September.

Route and Accessibility:
Bandaranaike International Airport in Colombo is the main international gateway to Sri Lanka. From Colombo, you can reach Jaffna and Galle by a variety of means including train, bus or car. Travel by train is scenic and recommended.

Accommodation and Booking:
Booking in advance is always recommended, particularly during the peak tourist season. Accommodations in these cities range from luxury hotels to budget guesthouses. Websites like booking.com or Airbnb are useful for reservation.

Clothing and Essentials:
Bring lightweight clothes made of breathable fabrics as the climate is generally warm and humid. Sunscreen, hats and sunglasses are essential to protect against the sun. Don't forget insect repellent, especially if you plan to visit rural or forested areas.

Health and Safety:
Ensure your routine vaccines are up to date before travel. Be aware that dengue fever is prevalent across Sri Lanka, so take measures to avoid mosquito bites. Tap water is not safe to drink, so stick to bottled water. Carry a good travel insurance that covers medical evacuation.

Local Etiquette and Respect:
Sri Lankans are generally friendly and polite. It's important to dress modestly, especially when visiting temples or religious sites. Shoes must be removed before entering temples. Tipping is not compulsory but greatly appreciated.