With all the components on screen, you should get a good indication of whether or not your parts will easily fit onto the size (and shape) of board that you require. If it looks like it’s going to be a tight fit then you know that you will have to work hard to try and keep the component spacing "tight", and the tracking as efficient as possible. If it looks like you have plenty of room then you can be a bit more liberal in your layout. Of course, if it looks like you have buckleys chance of getting your components on the board, you’ll have to go back to the drawing board.

Now analyse your schematic and determine which parts of the design can be broken up into "building blocks". Often this is fairly obvious. Say for example you have a complex looking active filter in your circuit. This would typically have a single input line and a single output line, but it will have lots of components and connections as part of the filter. This is a classic "building block" circuit, and one that lends itself well to combining all of these parts together in the same location. So you would grab all of these parts and start to rearrange them into their own little layout off to one side of your board. Don’t worry too much about where the actual block goes on your board yet.

You will also need to partition off electrically sensitive parts of your design into bigger blocks. One major example is with mixed digital and analog circuits. Digital and analog just do not mix, and will need to be physically and electrically separated. Another example is with high frequency and high current circuits, they do not mix with low frequency and low current sensitive circuits. More about this later.

As a general rule, your components should be neatly lined up. Having ICs in the same direction, resistors in neat columns, polarised capacitors all around the same way, and connectors on the edge of the board. Don’t do this at the expense of having an electrically poor layout, or an overly big board though. Electrical parameters should always take precedence over nicely lined up components.

Symmetry is really nice in PCB design, it’s aesthetically pleasing and just "looks right". If you have placed your components wisely, 90% of your work will be done. The last 10% should just be joining the dots so to speak. Well, not quite, but good placement is a good majority of your work done.

Once you are satified with the component placements, you can start to route all the different building blocks separately. When finished, it is then often a simple matter to move and arrange the building blocks into the rest of your design.

The Design Rule Check (DRC) will be covered later, but it is an essential step to ensuring that your board is correct before manufacture. A DRC basically checks for correct connectivity of your tracks, and for correct widths and clearances. Getting someone to check your board may sound like an overly bureaucratic process, but it really is a vital step.

No matter how experienced you are at PCB design, there will always be something you overlooked. A fresh pair of eyes and a different mindset will pick up problems you would never see.

If you don’t have anyone to check your board over and don’t have DRC capability, then you’ll have to do it yourself. Get a printout of your schematic and a highlighter pen. Now, compare every single electrical "net" connection on your board with the schematic, net by net. Highlight each net on the schematic as you complete it. When you are finished, there should be no electrical connections left that aren’t highlighted. You can now be fairly confident that your board is electrically correct.