This tutorial covers a whole range of tools the Sketchup-er has at his/her fingertips - most of them aren't immediately obvious, but can speed up modelling immensely. I'm going to assume you can already do the basics of Sketchup, if not check out this tutorial - Sketchup 1: The Basics - which takes you through the simple tools step by step.
This is a complicated sounding name for quite a simple thing, which is invaluable in creating neat models. In the last tutorial, we looked at how if you align a line you're drawing to one of the axes, it is highlighted in the relevant colour, and follows this direction exactly. The problem comes if you want to stay on that axis AND align with another point in the model. This is done by inference locking - when the line you're drawing becomes highlighted, hold down Shift. The line is then locked in this direction (it goes bold), and you can move your mouse to hover over another point to align to.
For example, in the situation below I want to draw a line going exactly vertical, which is the same height as the other line already coming up from the face. So, start drawing the line, and get it in the right place so it is highlighted blue (the text by the cursur will read 'On Blue Axis'). Then hold down Shift (the line turns bold) and move the mouse away to hover over the top of the other line. Once the inference has been picked up, the text by the cursur will read 'Constrained on Line from Point' - click to end the line here, and it will be the same length as the other one, and exactly vertical.
As well as locking to the axes, Sketchup can also snap to other directions, which can again be locked by holding down Shift. Two of the most useful of these are parallel and perpendicular snapping. These work in exactly the same way as the axis snapping, except the line is highlighted magenta. However, Sketchup will only remember the last line you drew - if you draw two lines at different angles, you will only be able to snap to the parallel and perpendicular directions of the second line. To get the magenta highlight, simply draw your line roughly in the same direction as the previous line (for parallel) or roughly 90 degrees to the line (for perpendicular) until it appears.
The Follow Me tool (accessed from the Large Tool Set toolbar) is similar to the Push/Pull tool, except that rather than just extruding the selected face straight out, you can extrude it along series of connected lines, allowing you to track the end shape around curves etc. This is useful for example, to create door surround details, since you can just draw the end profile, and follow a path around the outside of the door - Sketchup automatically sorts out the corners, saving you loads of time.
To start, draw your profile to extrude. Then draw your path to extrude along - make sure it connects at one end to the your drawn profile, and doesn't have any gaps in it. It also generally leads to better results if the first line is perpendicular to the drawn profile.
There are then two ways to use the tool. The easiest way is to first select the whole path (hold down Shift or Ctrl to select multiple lines), then click on the Follow Me tool from the toolbar, click on the profile and the final extrusion magically appears.
You can also start by clicking on the toolbar icon, then hover over the face to extrude. Click and drag the face along the path you want - the path will be highlighted red as you move along it, then let go when you've got as far as you want to go.
The Follow Me tool can also be used to create more complex curved shapes, such as spheres and cones, which would otherwise be impossible with the other tools.
To draw a cone, first draw a triangle, which is the profile to extrude. Then draw a circle with the centre at one corner of the triangle, and the radius the same as one side (this forms the path to extrude along). Then use either of the methods described above to sweep the triangle around the circle, hopefully forming a perfect cone.
If you extrude a face through another that's not connected to it, Sketchup doesn't automatically create lines where they meet, however this can actually be very useful. For example, you have a curved wall that you want to cut a hole for a window into - a tricky problem as drawing on the exact curves you want would be extremely difficult. However with intersect it's much easier.
First draw a face the size of the hole you want, making sure it's not touching the curved surface. Then extrude it through the curved wall using the Push/Pull tool - it will look something like this:
Next triple click on the original face to select the whole extrusion, then Right click -> Intersect -> Intersect with model (don't worry too much about the other options on the menu). Sketchup then adds lines where the extruded geometry meets that of the curved wall, which then allows you to delete as appropriate to make your window.
Another useful (but hidden) timesaver is array copy. We saw in the last tutorial how holding down Ctrl whilst using the Move tool allows you to copy geometry, but often there are times where you want lots of copies, all spaced the same distance apart. A good example would be making a staircase - the quick way is to just model one step, then use array copy to make all the others.
First model the bottom step, and copy it to make the next step by triple-clicking to select the whole thing, then hitting M and holding down Ctrl to place a copy in the desired place.
Once you've placed the second step, type in X followed by the number of copies you want (which includes the second step you just made). Hit Enter and the rest of the steps appear. This works best if each step is a component - see the next tutorial on efficient modelling.
Finally, a look at re-aligning the axes. Chances are that unless whatever you're modelling is very square, lots of the lines you draw won't be aligned exactly to the original axes. Since constantly rotating the right angle, or getting the parallel/perpendicular lines to show all the time is a hassle, sometimes it is simpler to just align the axes to whatever you're drawing. To do it, select a face to align to, then go Right Click -> Align Axes. Whilst the blue remains vertical, the red and green now track the angle of your face, making drawing in that direction much easier.