Making indented panel lines for 3d printing

I'm quite new to Blender but planning to use it for 3D printing, so I'm looking for a solution which will actually modify the geometry. I have created a couple of aircraft. I need to detail them with some panel lines but I don't know how to easily make an indented straight line.

• Looking at that model close up, the topology isn't so great. It seems to be made of all tris. I would recommend remodelling it as it is quite a simple shape. After that, take a look at the knife, inset and extrude tools. – iKlsR Nov 18 '13 at 11:52
• Thanks for the tip. I should have said, I'm aware the topology is shocking especially around the front where the wings start. As a beginner, I'm not sure how i managed to get so messed up around that area. Thanks, I will investigate those tools. – TimP Nov 18 '13 at 12:04

You might also be interested in the Inset tool. This can be useful for giving your faces a bit of distance from the sharp edges so any further modifications don't look odd or modify parts of the mesh you don't want. Press I while selecting multiple edge loops or faces and use your mouse to adjust the inset level.