a) You can either start your your exploration of Karnataka coast from either Mangalore or Karwar.
b) If starting from Karwar as we did
By Bus - There are overnight buses from Bangalore to Karwar both by KSRTC and Private operators
By Car - You can reach Karwar by any of these two routes
a) Bangalore - Shivamogga - Jog Falls - Honnavar - Karwar. Distance 520 KMs. Very good road till Jog Falls and
decent road beyond. Check road conditions before start.
b) Bangalore - Hubli - Yellapur - Karwar. Distance - 521 KMs Excellent roads. Check road condition between Hubli - Karwar
My recommendation is Option (a) which will help you see Jog falls and beautiful Sharavathi Valley on the way.
By Train - Not advisable as there is no direct trains to Karwar from Bangalore
c) If starting from Mangalore
By Bus - There are overnight buses from Bangalore to Mangalore both by KSRTC and Private operators
By Car - You can reach Mangalore on this route
a) Bangalore - Hassan - Sakleshpur - Mangalore. Distance Very good road except for a stretch of 20 KMs in Shiradi
Ghat which is not good. Check road conditions before start.
By Train - There is direct trains to Mangalore from Bangalore
Karwar - Number of resorts have opened in Karwar in recent times. Though expensive, Devbagh beach resort is the best.
Gokarna - Many choices including home stays available now
Murudeswar - RNS lodge or Naveen beach resort provide decent accommodation
a) Best season to explore the coast is November till February. It is hot from March to May and monsoons are heavy during June - September. Start early so that you can spend time to see Jog falls as well as Sharavathi valley. Stop over at a watch tower to see Sharavathi river taking a bend. Check the picture in this link http://www.flickr.com/photos/aithals/2477857666/
b) If you are planning to reach Karwar or mangalore by bus or Train, it is recommended that you hire a cab to tour the different places on the coast. though the bus services in coastal Karnataka is very good, this will help save time.
c) When you are driving on NH 17 between Karwar and mangalore, stop over to savour beautiful sights. The beautiful drive between Karwar and Ankola is now marred by the wall constructed by Navy. Nevertheless stop over and view the see from a height.
d) Gokarna may be crowded during festival season. You will also be troubled by priests who will try to influence you to do special pujas etc. avoid them.
e) One can definitely spend a day in Gokarna itself and enjoy Om beach. Hippies who used to crowd Goa, have moved now to Gokarna!
f) Do the trip leisurely and savour the sun rises, sun sets, rivers etc.......
g) If you are sea food or Chicken lover, don't forget to visit Shetty Lunch home in Kundapur.
h) If you are interested in snorkeling, scuba diving etc Devbagh beach resort and turtle bay beach resort organises it.
i) If interested one can take detour from NH 17 to go to Kollur and Idagunji to see famous temples of Mookambika and Ganesha
Some good web links which are helpful.
a) Wiki entries on Karwar, Gokarna and Murudeswar provide good information