Name the parties properly. A brand name on a letterhead is not always the legal person who can be sued, or who can sue. The signatory should have authority, and if they sign for a company it should be possible to see that they do.
Describe the work, the goods, or the service with enough detail that a stranger could tell whether it was done. Vague enthusiasm in a recital does not fix a missing specification. Dates belong in the same part of the document, including what happens if a date is missed.
Price, taxes, and payment are three different sentences. Say which taxes are extra, when an invoice may be raised, and what happens if it is paid late. A clause that quietly shifts every tax to the other side is easy to overlook and expensive to discover.
Say how the contract ends: on a date, on notice, or for a stated breach. Limitation of liability and indemnity clauses decide who pays if something goes wrong. They are often copied from another deal. Read them as if the loss had already happened.
Confidentiality, and the clause that chooses a court or an arbitration, decide the fight before the fight begins. A clause that sends a small Indian supply dispute to a distant seat of arbitration may be enforceable and still be a poor bargain. This is a reading list, not a template, and not a statement that any particular clause will be enforced in every court.