The IELTS writing exam consists of mainly two tasks- Task1, Task2. The IELTS writing task2 of General Test and Academic Test are the same, however, IELTS writing task1 varies.
Task1 basically examines your ability to scrutinize data in an objective manner, without providing an opinion and Task 2 needs a subjective piece of writing on a general topic. Task1 of General Test contains a letter, whereas, in task1 of Academic test, it is required to compare the information from the chart, table, graph etc.
This must be kept in mind that IELTS examiners are not testing your knowledge regarding the topic, instead of competence in the usage of the English language.
The minimum word limit for Task 1 in both General and Academic Test is 150 words and you must spend 20 minutes on this part whereas Task 2 must be of 250 words on which you should spend 40 minutes. There is no upper word limit in either of the tasks.
Rather than writing a good compacted essay, candidates write irrelevant lines just to increase the length of the task, as they believe that they will fetch extra marks for writing an extended essay, which is completely a blunder. It is very crucial to keep the tasks up to the word limit or perhaps a little more like you can attempt task1 in 150-180 words and task2 in 250-280 words. If your task will be under word-limit, you will lose the marks. While practising the tasks, you should count the number of words in the first line and then multiply it with the total number of lines you have written.
It is always better to spend some time to proof-read the task by checking your work. The writing test is not all about quantity, it is just about the quality and accuracy. Always bear in your mind that the more you write, the more chances are there of making a grammatical or spelling error.