Hello! That's a great choice of destinations in Indonesia. Here are some travel tips to help you plan your trip better.

Best Time to Visit:
The best time to visit Indonesia, which includes Jakarta, Bandung, Malang, and Bali, is during the dry season which is from May to September. The weather during this period is conducive for outdoor activities and sightseeing.

Route and Accessibility:
Start your journey in Jakarta, the capital city, which is easily accessible by air from most international destinations. From Jakarta, you can take a domestic flight or train to Bandung. A train journey from Bandung to Malang is picturesque and recommended. Bali, being a popular tourist destination, is accessible by air from various cities in Indonesia including Malang, or by ferry from some parts of Indonesia.

Accommodation and Booking:
There's a wide range of accommodations in all these cities to suit all budgets, from luxury resorts to budget-friendly hostels. It is recommended to book your accommodations in advance, especially during the peak tourist season. Websites such as Booking.com, Agoda, and Airbnb are popular for reservation.

Clothing and Essentials:
Carry lightweight and breathable clothing as Indonesia has a tropical climate. Don't forget to pack a good SPF sunscreen, a hat, and sunglasses. An umbrella or raincoat can be useful as sudden showers are common, and also carry a reusable water bottle to stay hydrated.

Health and Safety:
Make sure you're up-to-date on routine vaccines before every trip. These vaccines include measles-mumps-rubella (MMR) vaccine, diphtheria-tetanus-pertussis vaccine, varicella (chickenpox) vaccine, and your yearly flu shot. Most travellers also get travel vaccines for Hepatitis A and Typhoid.

Local Etiquette and Respect:
Indonesians are generally friendly and welcoming. In terms of etiquette, it's important to respect local customs and religions. Dress modestly, especially when visiting religious sites. Also, using right hand for giving or receiving is considered respectful.