Cd you please let me know how to travel by long-distance bus from Hongkong to Meixian (in Guangdong?

The bus takes about 6 hours.
The bus usually leave at around 07:40 and 14:40 at No., 22, Lai Chi Kok Rd.

Can the tickets be purchased on the spot?

It is hard to tell. The buses are only two, so it is suggested to book in advance, so that your plan will not be disturbed.
I used the bus in the peak season, so I have to book the bus in advanace.

Hi Ketty, where can we book the bus in advance? Any phone number or website?
I'm not stay in Hong Kong

From Lai chi Kok road, do you mean Lai Chi Kok Station or exactly in the road side?

Thanks

But as I know, the direct cross-boder coaches can be caught at the underground coach terminus at No. 8, Austin Road; the Guangzhou-HK coach ticket office near exit A of Prince Edward MTR Station and Wai Wah Centre, Sha Tin. You can go either of the places to find the buses. To consult details of the coaches, u can dial （852） 2559 8348 to ask. By the way, the coaches are operated by The Motor Transport Company of Guangzhou and HK Limited.