Sure, here are some travel tips for your visit to Cambridge, Oxford, and Bristol:

Best Time to Visit:
The best time to visit these cities is from June until September when the weather is warmest. Spring (April – June) is also a great time to visit when the cities are blossoming.

Route and Accessibility:
You can easily access these cities via train or coach from London. There are also direct bus services between Oxford and Cambridge. For Bristol, trains from London Paddington are fastest, taking around 1.5 hours.

Altitude and Acclimatization:
There's no worry about altitude in these cities. They are all at low elevations.

Accommodation and Booking:
Each city offers a range of accommodation options from luxury hotels to budget hostels. It’s best to book in advance, especially during peak travel seasons or during university terms.

Clothing and Essentials:
Pack according to the season. For summers, light clothing should be fine. But always keep a raincoat or umbrella handy as UK weather can be unpredictable. For winters, a warm jacket, gloves, and hats are necessary. Comfortable walking shoes are a must as these cities are best explored on foot.

Health and Safety:
The UK is generally safe. Just remember to follow common travel tips like keeping your belongings safe and having a copy of your important documents.

Local Etiquette and Respect:
When visiting the universities, remember to respect the academic environment. Some colleges may have restricted access so do check before visiting.

In Bristol, visit the Banksy walking tour but remember not to touch or tarnish any of his artwork. Also when in pubs or restaurants, keep in mind that the British often value politeness and queuing etiquette.

Cambridge and Oxford have a rowing culture, if you decide to participate or watch, remember to follow the safety instructions especially if you're new to rowing. Be aware that these cities are bike-friendly, so watch out for cyclists while you're exploring.

Remember to enjoy these cities which offer not only rich history but also lively cultural scenes and vibrant nightlife.