For Higher Tier accuracy is more important. Carefully check spelling, accents, gender, plurals and tenses.
Try to include different tenses if possible. You may be asked about what you did last weekend (past tense); try to add if you'll do the same thing next weekend (future tense).
As with the conversation part of the speaking exam, this is your opportunity to show what you can do. If you're not quite sure how to say something, write it another way:
e.g. You want to write: I invited her to go out but you can't remember.
You are in control. Choose what you are going to write according to what you are able to write in French.