it really helps to know a friend that knows your car inside and out.
I have a mk4 vw jetta. When I did my sub/amp a few years back, my friend helped me route all the wires cleanly. Since he already did the sub/amp in his jetta before, he knew where all the right locations for everything would be, how to pop the right panels, and things of that nature. Now after he helped me out, I learned a bunch of neat little tricks. Hell, when I ran wires for my fogs, I hid them completely out of sight and ran them along my wiring harness into my interior. No firewall drilling or need to find a grommet or anything (although the grommet that I know of is now packed with a boost gauge hose and a couple of other things haha)
Also take your time with everything. Its better to spend a few more hours of your time and have everything look clean than have something stick out or even short out and ruin your equipment, or even worse, your car.