Writing a conclusion is an important part of any piece of writing. It is often possible to get a good picture of an assignment by looking briefly at the conclusion. However, writing a conclusion can be quite difficult. This is because it can often be hard to find something interesting or useful to say in the conclusion. Conclusions should be attractive and interesting but often they are rather dull and "formula written".
Although formulae for writing conclusions are tempting to use, it is always best to avoid set phrases such as "Therefore, let us conclude that..." which are clichés, and do not help to end your work in the best light.