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For most symmetrical shapes I use a grid and guides. Change the settings of your grid what suits you best, make sure that snap to grids and/or snap to guides is selected and start drawing. For straight shapes it easy to use the Polygon Lasso tool. For irregular shapes, you can use the vector tools in Photoshop or use a program like Illustrator. If you have shapes that need some anti-aliasing, you can create a layer mask and blur the edges of the shape on this layer mask and add a levels adjustment.

It's also possible to draw shapes by hand using a mouse or a tablet. In all cases, working with guides/grid is an easy way to keep control over your symmetry. You can draw with selections, brushes, masks, vectors etc. You have to choose the method that suits you best.