If you are making a low offer, you can increase the appeal of your offer by strengthening your other offering terms....

DEPOSITS
Make the largest deposit you are comfortable with so the seller knows you have money "on the line" and that you won't risk losing that money by attempting to walk away from the deal.

CLOSING COST ASSISTANCE
Sellers don't just look at the contract price --- they calculate their net proceeds based on the offer price and any credits or closing cost assistance. Only ask for assistance if you truly need it.

FINANCING
Provide as much detail as possible about your financing intentions, and always include a pre-approval letter. Sellers who believe you are capable of financing the purchase will be less hesitant as they consider other terms of your offer.  And yes -- offer cash, a large pile of it, if you are able.  :)

PERSONAL PROPERTY
Don't automatically ask for everything the seller intends to convey --- if you don't need them all, leave them out of the offer. Allowing the seller to keep their washer/dryer (for example) may make them more flexible in other areas.

INSPECTIONS
Having a professional inspect the property you are purchasing is usually a good idea; however if you only intend to do it for informational purposes, consider leaving it out of the contract negotiations and conducting it post-settlement.

SETTLEMENT & POSSESSION
If possible, cater your settlement date and the details of transferring possession of the property to the needs or wants of the seller. This can go a long way towards gaining seller flexibility on other contract terms.

Finally, research the seller's context for selling. That information can be invaluable in negotiating a successful contract.