PR is part of the problem, but it's not really China's problem in that the key reason China gets such bad press is because the western mainstream press are fundamentally biased against China.
All they have to do is add 'state mouthpiece' to describe any news outlets remotely sympathetic to China and their brainwashed audience will automatically discount anything and everything said by those sources as they have been trained to do.
What China really is lacking in its diplomacy that is the chief cause of others taking liberty is a lack of use of its stick to punish those that cross it.
Sadly, China is behaving too civilised in the power based world we currently live in.
The so-called rules based world order simply does not exist so long as the US and its allies treat international laws as only something that happen to countries they don't like.
The likes of Vietnam, the Phillipines and India think they can push China around because China doesn't want to hit them.
No amount of PR or talking will get them to change that view. The only way to get them to change their behaviour is if China makes it clear that there will be real and immediate costs to crossing China, as the US demonstrates at every opportunity.
But then, China will end up being no better than the US if it behaves that way.
That is true, China's foreign policy during the last 20 years (except for last 5 years) has been really mellow and weak. This is the reason that weak nation such as Philippine, Vietnam can openly challenge China because they think China cares too much for peace, and they were betting that with US's backing, they can gain advantage from China without firing a shot, due to China's overwhelming importance on the emphasis on peace.
But they miscalculated, not did China not roll over as expected per China's previous behavior, instead it pushed back harder than ever before and this surprised them, so then they ask US to directly intervene and all US can do is send ships once every few weeks/months. I think finally China has demonstrated to the world that, yes I want peace, but not peace at the expense of my territory integrity and core interest.
I think the next killer move for China is to work with Philippine and joint develop SCS with full Chinese control, but give Philippine a big share of the profit, to send out a message to the rest that if you work with me, I will help you, I will share my pie with you. However if you work against me, there will be no pie for you. Philippine and China should joint develop part of SCS that are disputed with Philippine and Vietnam, and cutting Vietnam's share to 0, this will force Vietnam to work with China on other parts of SCS and China then can offer the same to Vietnam as well, but if Vietnam disagrees, China should go ahead and start to develop on its own or with another 3rd party in SCS.
Basically now China need to send out a message that whoever cooperate and come to my side sooner will enjoys more benefit, but the longer you wait, the less I will give you, and if you don't come to me at all, there will be NOTHING left for you.