1. You should know that you will be awarded 3 marks for the format and 12 marks for the content. This is where you can score. Just make sure that you fulfill all three format requirements; for example, for informal letter you must have your address on top right, 'Dear ___,' before the opening of your letter, and your signature at the end of the letter. Then, make sure that you mention all the 12 points given and you will get your 12 marks for content. However, sometimes only 10 points are given and you will have to give two more on your own. You might also be given 6 points only. In this case, you will have to elaborate on each point to make sure that you get 12 marks altogether for the content. So now you have 15 marks already.
2. As for the language, it depends very much on your grammar especially the tenses (sad to say in Malaysia, the marking criteria concerns more on identifying your mistakes and less on your creativity). Apart from that, if you are able to elaborate well on the points and provide relevant examples, your language marks will be higher. The full mark for language is 20. Average students will usually get around 10-13 marks while the good ones will get around 15-17.
3. It is important for you to score at least 25 marks for Directed Writing, since it is one of a few sections in SPM English 1119 paper where one can do without struggling. My advice is not to waste the precious marks by not taking this section seriously. Directed Writing means the directions are all given, so just follow them and get there. Get what I mean?