If motivation is an issue with regards to writing, you might like to base the tasks on interactive activities. 

Below are 3 suggestions, but the key to all of them is that they involve Ss writing to each other, reading one another's work, then writing a response. 

In all cases, you can have them do editing, self-correction or peer-correction at more than one point.  You could have them focus on punctuation and linking words at these points.  Alternatively, you could collect their papers and use or adapt them for attention to punctuation and linking in later lessons.  You could also pre-teach key aspects of punctuation or linking before each task.  The tasks themselves, though, focus more on keeping the Ss engaged and motivated in writing.

Messenger/ICQ/Skype chats 

Pairs pass a lined sheet of paper between them mimicking online chat.  Each time they write to their partner they may use only two lines, so the writing takes on a short, conversational tone. 

This works best if they are seated on opposite sides of the room from their partner and the teacher acts as 'the Internet' by passing the paper back and forth between them.  And to stop Ss from getting bored when it's not their turn to write, you can encourage them to make notes about what Qs to ask next, etc.

After they've written back and forth about 5 or 6 times they group up with other pairs and compare their conversations. 

Complaint & Acceptance/Rejection

Build up two situations.  In both situations Mr/Ms X has a broken product that was made by Company Y.  However, in one situation it is broken because of a fault with the product itself (so Company Y is to blame), and in the other situation it is broken because Mr/Ms X was careless, but he blames Company Y anyway. 

Example:

Mr Jones bought a Sony Digital Camera.  The camera has a special 'tough' design and the advertisement for it says "even if you drop the camera it will be okay" - and it is guaranteed to survive a typical fall.

Situation A (faulty product):  Mr Jones was taking a photo of his family in a restaurant and dropped his camera.  It broke.

Situation B (Jones' fault):  Mr Jones was riding a horse while trying to take photos and dropped his camera.  It broke.

Each S secretly chooses one situation and writes a letter of complaint to Sony.  The letter of complaint includes the 3 stages: a) summary of problem; b) background/what happened; c) demands/requests.  In section (b) they must include where they were and how they dropped the camera.

Once finished, Ss exchange letters with a partner.  Now they have to read the complaint letter they receive and write a reply.  But for the reply, they have to choose whether to reject or accept the complaint.  For a rejection: a) express sympathy; b) explain why it's not Sony's fault; c) offer a solution or suggestion.  For acceptance: a) apologise; b) explain why there was a problem; c) say how you will compensate the customer; d) apologise again.

Letter to the Editor

Do some reading tasks involving 3 short news items of different fields, eg. politics, technology, and celebrity gossip.  (Get these from a real newspaper/online news, then adapt them to simple 5-6 line summaries).

Ss must then choose one of the 3 articles, and write a 'letter to the editor' in which they disagree with and/or ask questions about the article.

Once they've finished, they exchange with a partner.  Now they have to read the letter they have received and write a reply 'from the editor'.  In the reply they have to respond to any disagreement with an explanation or apology; and to any question with an answer.  For effect, at this stage Ss can be encouraged to write with slanted writing, like italics, and include it on the same sheet of paper as the original. 

Ss can then share and compare letters to and from the editor with other groups.