When we write an informal letter of advice, we usually write four paragraphs. In the introduction we express sympathy and say that we understand the problem anor that we think we can help. In the main body (Paras 2-3), we make suggestions and give our reasons. We write each suggestion in a separate paragraph. In the conclusion, we write our closing remarks, and sign off.
I am so glad to hear that you have decided to move to London, it'll be great to have a friend from home living here. We'll be able to do things together like we used to. In your letter you asked me to give you some advice about finding a flat; here are some suggestions.
If I were you, I would start by checking the classified advertisements in the London papers. For example, the 'Daily Mail' and the 'Evening Standart' have large sections with houses and flats for rent. That way, you will be able to see what is available for rent at the moment.
Another good idea is to contact an estate agent. Goldshmidt and Howland have offices all over London. That way you can get a list of all places in the area you want at a price you can afford.
I hope this helps. Please let me know how things turn out. If you need anything else, please call.