This year has already been kickstarted by an unannounced visit by Marshall Kim Jong Un to Beijing where he met with President Xi. This meeting was largely expected to occur in the run-up to any significant summit with the United States. Last year 3 visits to China took place where the two leaders met and likely discussed developing a coordinated strategy for ongoing bilateral talks between the DPRK and US administrations. So what benefits exist for Pyongyang in building closer diplomatic ties with the Chinese government?
At this moment in time the most pressing issue for Pyongyang is the denuclearisation issue. One of the few statements released from the meeting between the leaders through state media was from China calling on the US and DPRK to "meet in the middle" in future talks. China is one of the worlds foremost powers and so a statement calling on the US to be prepared to make significant concessions in future meetings will carry more weight in Washington than any statement out of Pyongyang. The development of a Sino-Korean diplomatic strategy, which will likely be implemented in future summits with the US, means that any concession demands from Pyongyang will carry with them the tacit backing and support of Beijing. China and the US are currently engaging in economic talks in an effort to stop an ongoing trade war which is damaging the US economically. Turning Beijing against Washington by refusing concession demands from the DPRK may hinder progress in those trade talks and so by working closely with China Kim Jong Un has just given himself more leverage which he can bring to the table in a future summit with President Trump.
There are also many symbolic reasons for such a summit with President Xi Jingping. It is in the interest of the DPRK to keep its economic options open. If the US administration feels that it alone holds to key to economic development in the DPRK they will be able to use that to their advantage in talks and demand concessions from Pyongyang in exchange for economic aid. This trip demonstrates that the relationship with communist China is still strong and that the DPRK does not need to rely on Washington to rescue its economy. This benefits China as well, allowing it to portray itself as the only country which has the ear of Pyongyang, something which it could use as leverage in its own talks with Washington.
Another summit being planned, according to some reports, is a trip to Moscow by Marshal Kim Jong Un to meet Russian President Vladimir Putin. Russia and the DPRK have maintained a rather friendly relationship with Putin visiting Pyongyang in 2000. Building close ties with Russia and China, two permanent members of the UN Security Council, would be a very sound move on Pyongyang's part as they have the power to block new multilateral sanctions against the country. Closer ties with Russia could also provide another route through which the economy could begin to recover. The USSR was the primary force behind the economy of the DPRK in the mid-20th century when Pyongyang was outperforming Seoul and so attempting to replicate that economic support from Russia would allow Pyongyang to advance its economy-first policy. They could even play Moscow against Beijing forcing the Chinese to become more involved in the DPRK's economic development in an effort to preserve their status as the only country who have control over Pyongyang.
In short, everyone is trying to get more leverage over the other before they enter into talks. Donald Trump won't wish to risk aggravating the Chinese by being too dismissive of any demands for concessions from Kim Jong Un since damaging the relationship with China could have a direct impact on the trade war negotiations. From Pyongyang's perspective, the more options on the table, the less beholden it is to any specific country and the more power it has in ongoing negotiations. We won't know how well this tactic will play out for North Korea but a second US-DPRK summit seems imminent, the result of which may be greatly influenced by this summit with President Xi.