There are all kinds of die-cast cars and other kinds of models that are available in the market. See what you or the person for which you are looking to buy likes. Go ahead keeping the specific likes and dislikes in mind.
See that current collection that you might already have in order to make sure that you do not buy a duplicate die-cast model. It is a good idea to make a list of products that you are interested in before you go shopping to avoid the trouble later on.
Die-cast models are built on a scale. Often people are collecting models that are based on a certain scale. Make sure that the model that you are planning on buying meets that particular scale so that you do not have something that is out of place.
Keep these in mind particularly if you are looking to start collecting these models. It will be ideal that you start from lower priced models and as you learn more about the different qualities of each kind of model, you can go ahead and spend more.
Try all Kinds
Make sure that you do not restrict yourself to a certain kind of vehicle. Having a diverse collection can help, particularly if you are looking to collect these to resell. Getting vehicles such as fire trucks, monster trucks and off course the Harley Davidson motorcycles can add a lot more value to your collection of the die-cast models. You can also opt for planes and tanks or what not.
Know the Trends
It is important that you know the trends that are currently in. You can join a collectors group or an internet forum to stay up to date with the latest information. This will be a great way to stay in touch with the field and even get some great tips.