Turbulence is largely random. Some pilots will do more to go around potential sources of it while others won't (due to fuel cost and scheduling reasons or the generally correct perception that it's not necessary to do so) but it's always at the pilots' discretion, never a publicly-stated policy by an airline, so you can't do much to control for it. In any case, violent turbulence is usually sudden but short and unlikely to cause any problems, so from the pax's point of view all you can do to mitigate it is to stay buckled up while in your seat and other than that learn to live with it.

Perhaps you should be more concerned about regional weather patterns as they have the potential to wreck your itinerary and experience. In East Asia, there's the typhoon season, which can lead to travel disruptions. In Singapore, the air can be bad for parts of the year due to forest fires in the neighboring Indonesia. In Thailand, especially the northern part, you don't want to visit during the time when farmers set their fields on fire, ruining air quality. Other areas yet, like southern Thailand or Vietnam are likely to experience incessant rain during parts of the year, which can also cause flooding. And regardless of the weather, you want to avoid travelling to places Chinese people would visit during the Chinese New Year as they're going to be heavily congested.

Not sure if it's being helpful but there is no sure way to avoid turbulence so if you really dislike it you could consider choosing your destinations so as to limit the number of flights. For example, of the places you mentioned, you could easily travel between Singapore and Kuala Lumpur overland.