what are the simple steps to draw a neat and labelled diagram of heart and brain in  short time?

You can follow the steps given below:

For human heart:

• You can draw the outline of the chambers of human heart first.
• You can draw the auriculo-ventricular septum to divide it into two halves.
• Then draw the arteries and veins associated with the heart.
• Then draw the valves present in the heart.
• Finalise your diagram and then add the appropriate labels.

For human brain:

• You can draw the outline of the human brain first.
• Begin by drawing to concave shapes or half-moon shapes. Draw a larger one for the cerebral cortex of the brain and then a smaller one on its lower right side for its cerebellum.
• Draw swirly lines on the left-side of the brain.
• Draw the right-side of the brain by drawing again the swirly lines.
• Draw thin and compact lines on the smaller concave shape of the brain or on the cerebellum.
• Draw the spinal cord on lower-middle part of the brain.
• Finalise your diagram and then add the appropriate labels.

Make sure to practice drawing the diagrams regularly.