Always call or email the advertising agent to check any missing information. As soon as you have established the property has potential, book a viewing with the agent. Don't forget to take a camera and tape measure on every viewing you go on.
Remember - buy-to-let properties are not emotional purchases. So be sure to remain rational about what is right for the rental market, not yourself.
Your position - buyers with pre-arranged mortgages have a head start on most of the competition. If you've a buy-to-let mortgage sorted, make the agent and seller aware of this as it can put you in a favourable negotiating position.
Your budget - decide your maximum limit from the start and stand firm - after all you've done your maths and know the investment's potential. If the seller refuses to budge, you need to think very carefully if the property really is worth the extra money.
Seller's position - are they in a hurry to sell or have they been trying to sell for a long time? If so, they may be willing to accept a lower offer to make the sale. Sellers who are not in a hurry to move are more likely to hold out for a higher price.
The market - in tougher times when there are fewer buyers, sellers may be more willing to negotiate on price. Once you make an offer make it clear that it's subject to contract and a satisfactory survey.