A lease is read exactly once, usually standing up, usually while the person who wrote it waits. That is a poor moment to be discovering what it says, and it is the only moment most people get.
Ask for a copy the day before. A landlord or agency who will not send one in advance has told you something useful for free.
The clauses that actually decide things
Term and notice. How long the agreement runs, and how much notice each side must give. The two are often different. A tenant on a one-year term with three months' notice is committed differently from one with one month's. Check whether it renews automatically and on what terms.
What the rent covers. Rent alone, or rent plus water, garbage, security, service charge? A figure that sounds high with everything included may be cheaper than a low one with four extras billed monthly. Ask for the recent actual amounts of anything variable, not the estimate.
How rent can change. Whether there is a review, when, and by how much. "Subject to review" with no cap or notice period is an open door. A stated percentage or a stated notice period is a fair thing to ask for.
Who fixes what. Structure, plumbing, roof and the things that came with the unit are normally the landlord's; consumables and damage you cause are normally yours. What matters is that the agreement says so, and that there is a stated way to report a problem, not just an understanding.
The deposit. How much, what can be deducted, and how long after you leave it is returned. A defined return period is worth more than a friendly assurance.
Late payment. Whether there is a penalty, how it is calculated, and from which day. A flat charge and a compounding one are very different animals over six months.
Ending it early. What happens if you have to leave: a stated break clause, a penalty, or liability until the unit is re-let. This is the clause nobody reads and the one most likely to cost money.
Two things to check outside the document
Who you are dealing with. Is the person signing the landlord, or an agent with authority? If an agency, get the name of the company on the agreement. Money should go to an account in that name.
Whether the document matches the conversation. If you were promised the wall would be repainted or the tank replaced, it goes in the agreement or it did not happen. "They said they would" is not a term.
Before you sign
Get the version you are signing, in full, with any handwritten changes initialled by both sides. Keep a copy, and photograph every page if you are not given one.
Then do the move-in ritual: photograph the unit's condition, photograph the meters, and send both to the agency the same week. The lease sets out what you agreed; those photographs are what settles it later. See what a deposit is actually for for the rest of that routine.