Introduction
I've been using LaTeX for 15 years, but one year ago I started to write for the first time in my life a real book for students. So I followed usual widespread conviction: concentrate on the contents, the LaTeX will take care of the rest. However, this conviction holds only if you are writing a thesis or an article, where styling is largely unimportant (who reads theses anyway?).
Namely, after finishing my writing after one year of work I was into a real unpleasant surprise. I've received a modest lump of money to find a designer for a book. There is a big pool of good book designers out there, but not one has ever wrote a command in LaTeX. Which in fact means one year of intensive work shall be retyped in some other LaTeX incompatible program, figures shall be rescaled together with fonts... and everything I was so damn careful for over a year will be messed up in a second...
Question
Is it possible for a non-professional semi-experienced LaTeX user to implement design ideas to the document himself and save his precious work? Which document class should s/he start with?
To demonstrate poor performance of standard LaTeX classes for book design, I will show you part of the code written using KOMA-Script scrbook and approximate proposition from the designer.
Minimum working example:
\documentclass[12pt,parskip]{scrbook}
\usepackage[cp1250]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{amsmath}
\input{slike_1} % TikZ pictures
\begin{document}
\textit{Enakomerno večdimenzionalno gibanje} označuje gibanje, pri katerem je vektor hitrosti konstanten. Gibanje tem primeru opisuje enačba, ki je posplošitev enačbe~(...)
%
\begin{equation}
\vec{r} = \vec{v} t + \vec{r}_0,\label{k-umm}
\end{equation}
%
kjer $\vec{r}$ označuje trenutni, $\vec{r}_0$ pa začetni položaj telesa. Vektorju $\text{r}$, ki označuje položaj telesa, pravimo tudi \textit{krajevni vektor}.
\textit{Enakomerno pospešeno večdimenzionalno gibanje} označuje gibanje, pri katerem je vektor pospeška~$\vec{a}$ konstanten. Gibanje v tem primeru opisujejo enačbe, ki so posplošitve enačb~(...)
%
\begin{align}
\vec{r} &= \tfrac{1}{2} \vec{a} t^2 + \vec{v}_0 t + \vec{r}_0\label{k-uamm1}\\
\vec{v} &= \vec{a} t + \vec{v}_0 \label{k-uamm2}\\
v^2 &= v_0^2 + 2 \vec{a} \cdot (\vec{r} - \vec{r}_0) \label{k-uamm3}
\end{align}
%
kjer so $\vec{r}$ trenutni in $\vec{r}_0$ začetni krajevni vektor telesa, ter $\vec{v}$ trenutni in $\vec{v}_0$ začetni vektor hitrosti telesa. Pri tem je tretja enačba izpeljana iz prvih dveh.
\begin{figure}[!ht]
\centering
\Tpro
\caption{Poševni met}
\end{figure}
Če se telo nahaja v bližini Zemeljske površine, nanj deluje konstantni pospešek prostega pada $g = 10$~m/s$^2$ navpično navzdol. Vsako tako gibanje telesa je dejansko \textit{dvo}-dimenzionalno, saj se telo giblje po navpični ravnini. Po dogovoru $y$~os usmerimo navpično navzgor, torej nasproti smeri pospeška prostega pada ($\vec{a} = - g \vec{j}$), $x$~os pa tako, da začetna hitrost leži v $xy$ ravnini $\vec{v}_0 = v_{x0} \vec{i} + v_{y0} \vec{j}$. Potem lahko vsako od enačb~(...) razstavimo na \textit{dve} skalarni enačbi in dobimo
%
\begin{align}
x(t) &= v_{x0} t + x_0, \label{k-prsx}\\
y(t) &= -\tfrac{1}{2} g t^2 + v_{y0} t + y_0, \label{k-prsy}\\
v_x(t) &= v_{x0}, \label{k-prvx}\\
v_y(t) &= -g t + v_{y0}. \label{k-prvy}
\end{align}
Pri tem smo upoštevali, da je pospešek v $x$~smeri enak $a_x = 0$, pospešek v $y$~smeri pa $a_y = -g$, kar pomeni, da imamo v $x$~smeri enakomerno gibanje, v $y$~smeri pa enakomerno pospešeno gibanje.
\end{document}
Result of MWE

I think you agree with me this is totally unacceptable for a real book. The text is just too crowded, it gives 80-90 characters (including spaces) or 70-80 characters per line, and cca. 44 lines per page. I must agree with designers, this is just too crowded and unattractive for a university-freshman learning book.
Here is one of possible book designs:

EDIT: Since PGFTricks provided a bounty, I provide here the code for the picture, so you can test your ideas. It is scalable, \lmet provides the size of picture, \lms the lengths of vectors.
\tikzset{avec/.style = {->,green!75!black,line width=\wvec}} % acceleration vector style
\tikzset{vvec/.style = {->,red,line width=\wvec}} % velocity vec tor style
\tikzset{vlin/.style = {red}} % velocity vector style
\newcommand{\rang}[3]{
\begin{scope}[shift={#1},rotate=#2]
\draw[#3] (5pt,0) -- (5pt,5pt) -- (0,5pt);
\end{scope}}
\newcommand\Tpro{
\begin{tikzpicture}[>=stealth,auto]
\def\lms{0.005cm}
\def\lmet{0.0007cm}
\draw[->,very thin] (-500*\lmet,0) -- (13000*\lmet,0) node[right] {$\scriptstyle x$};
\draw[->,very thin] (0,-500*\lmet) -- (0,5000*\lmet) node[above] {$\scriptstyle y$};
\draw[very thin] (500*\lmet,0) arc (0:60:500*\lmet);
\node at +(30:500*\lmet+8pt) {$\alpha$};
\draw[vvec] (0,0) -- +(60:360*\lms) node[midway] {$\vec{v}_0$};
\draw[vlin] (0,0) -- +(180*\lms,0) node[midway,swap] {$v_{x0}$} -- +(60:360*\lms) node[midway,swap] {$v_{y0}$};
\rang{(180*\lms,0)}{90}{vlin};
\draw[vvec] (2372*\lmet,3240*\lmet) -- +(180*\lms,180*\lms) node[midway] {$\vec{v}_1$};
\draw[vlin] (2372*\lmet,3240*\lmet) -- ++(180*\lms,0) node[midway,swap] {$v_{x1}$} -- ++(0,180*\lms) node[midway,swap] {$v_{y1}$};
\rang{(2372*\lmet+180*\lms,3240*\lmet)}{90}{vlin};
\draw[vvec] (5612*\lmet,4860*\lmet) -- +(180*\lms,0) node[midway] {$\vec{v}_2$};
\draw[vvec] (8852*\lmet,3240*\lmet) -- +(180*\lms,-180*\lms) node[midway,swap] {$\vec{v}_3$};
\draw[vlin] (8852*\lmet,3240*\lmet) -- ++(180*\lms,0) node[midway] {$v_{x3}$} -- ++(0,-180*\lms) node[midway] {$v_{y3}$};
\rang{(8852*\lmet+180*\lms,3240*\lmet)}{180}{vlin};
\draw[vvec] (11224*\lmet,0) -- +(-60:360*\lms) node[midway,swap] {$\vec{v}_4$};
\draw[vlin] (11224*\lmet,0) -- +(180*\lms,0) node[midway] {$v_{x4}$} -- +(-60:360*\lms) node[midway] {$v_{y4}$};
\rang{(11224*\lmet+180*\lms,0)}{180}{vlin};
\draw[avec] (5612*\lmet,2430*\lmet) -- +(0,-180*\lms) node[midway] {$\vec{a}$};
\draw[densely dashed] (0,0) parabola bend (5612*\lmet,4860*\lmet) (11224*\lmet,0);
\filldraw[thick,fill=white] (0,0) circle (100*\lmet);
\filldraw[thick,fill=white] (2372*\lmet,3240*\lmet) circle (100*\lmet);
\filldraw[thick,fill=white] (5612*\lmet,4860*\lmet) circle (100*\lmet);
\filldraw[thick,fill=white] (8852*\lmet,3240*\lmet) circle (100*\lmet);
\filldraw[thick,fill=white] (11224*\lmet,0) circle (100*\lmet);
\end{tikzpicture}}

DIV=7to the document class options and then changing the number to your taste (IIRC 9 is default and smaller numbers give larger margins). Have a look at the KOMA manual (entertexdoc scrguienon the command line to open the documentation if you are using TeX Live) to find all these configuration options. – Chris Sep 25 '13 at 16:25\recalctypeareaafter all font settings, that can help. See the manual for more information on that … – Tobi Sep 25 '13 at 16:32memoir. I'm a big fan; you may like it. – Brent.Longborough Sep 25 '13 at 19:25