1- First of all arrange concrete molds into the shape, as you desire for your blocks. They are easily available and you can easily purchase them from different outlets.

2- Mix cement with sand by using concrete mixer. If your requirement is normal type of block, then use 3 parts sand and 1 part cement, but if you required stronger concrete blocks then use 1 part cement and 2 parts sand.

3- Now add crushed limestone or gravel into the mixer. The ratio is 1 part cement, 2 parts sand and 3 parts gravel, or roughly you can say that gravel should be equal combined sand and concrete mixture. If gravel quantity increases you may not get smooth surface and all effort will be wasted.

4- Add some water into the mixture, stirring it until it reaches the right consistency. You can check as you stir by scooping a sample of the mixture into a slump cone, measuring it it off and seeing how much the mixture settles. When it settles about 3 to 4 inches into the cone, the mixture contains the right combination of ingredients. Continue mixing the concrete for several more minutes until it is consistent throughout.

5- Spray the inside of your mold with a water-based concrete-releasing agent. This will let you remove the precast concrete block from the mold once it has hardened.

6- Pour the concrete carefully into the mold, then level it off the top using a trowel or a wooden board. Tap the mixture to help it settle, and to get rid of any air pockets in the mold.

7- Let the concrete harden for at least 24 hours before attempting to remove it from the mold. Then press down on the completed block while simultaneously pulling up on the mold. The block should spring free, and the mold can then be reused to make more blocks. Once you have set the concrete in the molds, clean everything up very quickly. Concrete is much easier to get off clothes and equipment when it is still wet. For more help and to get best blocks check Concrete Manufacturers.