Sure, visiting Tripoli, Ghadamis, and Tobruk is a great idea to explore the ancient history and rich culture of Libya. Follow these tips for a safe and enjoyable trip:

Best Time to Visit:
The best time to visit Libya is in the spring (March to May) or in the fall (September to November). The weather during these times is pleasant and suitable for sightseeing.

Route and Accessibility:
All three cities have airports and are accessible by road. The Great Man-Made River Project makes these desert cities more accessible. However, road conditions can be harsh and unfavorable, hence, hiring a local guide or joining a tour group can be helpful.

Altitude and Acclimatization:
There is no major issue related to altitude in these cities. However, due to high temperatures in summer, it's best to stay hydrated and take frequent breaks during sightseeing.

Accommodation and Booking:
Accommodations range from budget to luxury hotels in Tripoli. However, in Ghadamis and Tobruk options are more limited. It is advisable to book your accommodations in advance.

Clothing and Essentials:
Libya is predominantly Muslim, therefore dress modestly especially when visiting religious sites. Carry sunscreen, hats, and sunglasses to protect yourself from the harsh sun.

Health and Safety:
All travelers should have comprehensive travel insurance. Basic medical facilities are available but quality varies. Hospitals may expect immediate cash payment for services. Also, note that emergency assistance might be limited.

Local Etiquette and Respect:
Show respect for religious beliefs, especially during the month of Ramadan. Avoid photographing people without their permission.

NOTE:
Check for travel advisories as political instability and conflicts are a concern in Libya. Travel may not be advisable in certain regions and during certain times. Always put personal safety as the top priority.