Offers are best presented in writing in a formal email and not by phone or on a piece of paper in a restaurant. Explain your considerations for making an offer and give your thoughts and reasonings how you have arrived at such and such figure or terms. Your offer needs to be explicit when it comes to the price you are presenting and how you propose to pay for it. Make sure you mention any conditions for the purchase, like due diligence and the time you will likely need to conclude that. Also, mention that you are willing to make a down payment (typically up to 10% of the purchase price) to reserve the property and take it off the market for the time you are conducting due diligence. This shows you are serious when you present an offer. If you have a notary of your choosing, mention that and explain how you propose to pay for his fees. Also, it’s best you mention the taxes both parties will be subject to. This shows that you understand the mechanics of a sale and establishes you as a bona fide buyer.
Your offer may not be accepted right away but be countered by a counter-offer from the seller. You may then gauge the wiggle room you have to come to closing the deal. If the gap is too large in your opinion, it is sometimes worth to wait a while with providing another offer. Just acknowledge receipt of the counter-offer and say that you will consider it. The vendor may get back to you and improve his counter-offer without you doing much.