Mental activity and mental impression are to be clearly distinguished. When native speakers won’t have any confusion as to what style should be used, foreign speakers are most likely to find it a hard nut to crack.The examples given below will elucidate the usage.

• I am thinking about the project we are planning to execute. (This is a mental activity. Here one is in the activity of thinking that can be explained progressively)
• I think you are right. (Here, one is not thinking about anything, rather this is a mental impression and the conclusion about a particular idea has been reached.)

Note :  Now the difference between ‘I am thinking’ and ‘I think’ is clear from the above examples. Normally only these two differences need be studied.  But there can be situations when one might be more puzzled or confused to hear “I am thinking you are right”.  Normally we don’t come across  situations like this. But that can be perfectly correct if the speaker is deliberately choosing this form to suggest that a certain conclusion is forming itself in their mind but is not yet final.

• I like my work. (This impression is final and therefore no vacillation as to whether I like the work or not.)
• I am liking my work. (suggests that the process of becoming adjusted to it is still going on)

However, until you are thorough with the differences between the usages the learner is advised not to use the progressive tense in both the cases.