Personal pronouns (like I, we, and you) are important in letters and memos. In such documents, it is perfectly appropriate to refer to yourself as I and to the reader as you. Be careful, however, when you use the pronoun we in a business letter that is written on company stationery, since it commits your company to what you have written. When stating your opinion, use I; when presenting company policy, use we.
Since your signature is likely to be difficult to read, type your name down a couple of lines so that your reader knows who is writing to them. Enclosures: (Below signature block) If you have included any further material _ a business card, a brochure, a price sheet, whatever _ list the number of items and describe each. Finally, proofread, proofread, and proofread again. While a friend might excuse even the worst spelling and grammar, a business letter is often your first (and maybe only) chance to make an impression _ it needs to be impeccable.