Ferrous metals, like ferrous steel, are often worth more at the scrap yard than non-ferrous metals, like aluminum. So if you only have limited time in your day to collect scrap metal and take it to the scrap yard, focusing on finding ferrous metal is a good approach. So where can you find such metal?
Old Farm Equipment
Old farm equipment was often made with steel, and each piece of farm equipment contains a lot of it — so you get a lot of bang for your buck as long as you have a large enough truck to get the equipment to the scrap yard. A good way to find old farm equipment is to drive around rural areas and look for pieces buried in weeds and brush. Knock on doors, and offer to take it away. Often, the owners will be glad to have the equipment off their property, and you won't have to pay a dime.
Another good source of steel is old, worn building support beams. If you see any buildings that have collapsed, inquire with the town who they belong to, and contact the owners. They might let you take any steel you can find provided you also help clean up the site. Do not enter abandoned or damaged buildings without permission; you never know what is safe.
Today's appliances are often made with a type of stainless steel that is non-ferrous, or in other words, non-metallic. But old appliances were generally made with sturdier, ferrous steel. You can find tons of old refrigerators, ovens, furnaces, and other appliances if you just drive around neighborhoods in the spring when people are replacing their older items. If an appliance is set out for the trash, it is fair game for you to take. If you're not sure whether it has been set out for the trash or for sale, there's no harm in asking. You could also place an ad online telling people that you will come and pick up their old appliances. Expect a lot of calls — people would rather just have this stuff gone rather than hold onto it until the town can pick it up.
Ferrous metal recycling brings in a pretty penny at most scrap yards and recycling plants. If you source multiple places for these metals, you should come across plenty of metal and have no trouble filling up your truck.