If you only work in Dehong prefecture on the border between China and Myanmar, you don't need any formalities in Myanmar. Just enter China and get the entry permit. Then go to the public security bureau to apply for a temporary residence permit (term 1 month, renewal for 3 months), and if necessary, you must show your health certificate (go to the health bureau for blood test). It's about 100 RMB, 10000 Myanmar Dollar. Just some blood tests cost about 70 to 80 yuan. Some Burmese here don't have temporary residence permits. Although the investigation is not so strict, it will be troublesome if you are caught (China police are very cruel to Burmese).
If you want to work here, I suggest you apply for a temporary residence permit, so it won't be difficult for you to stay in China. I don't know what procedures to go through if I want to work in the mainland of China.