Try to observe the people and nature around you. Try to imagine how you daw all single things like cars, trees, houses,.... . Practice drawing all these little daily seen objects. For comics it is necessary that you can draw everythimg.
A easy way to get the antomy of human is through catalogs of bath clothing or bodybuildermagasines because you see the muscels of a human in work and flexed.
Some general tips for sketching are to keep your lines thin and loose. Try to make round curves and get some flow into your drawings. Make more than one line. The first thing of a drawing should ever be a rough sketch of the action you want to draw. This is nessacary to keep your aim in the eyes. Try to keep this sketch as rough as possible. Don't go into details the first time you draw your scene.
In acomic everything have to look real and original. A easy way of drawing the things naturally is to look in magasins or the internet for the objects you need.You can put them under a few categories like fourniture, vehicles,... . And under all this subjects you can go more in detail vehicles : cars ships planes bikes motorbikes. With the photos of all these tings you will be able to draw the things more realistc(and esaier).