A neat way of deciding which higher-dimensional theory to start from is to count the number of spinor components.  In ten dimensions, a spinor has $2^{[d/2]} = 32$ components (complex) which are reduced to 16 after imposing the Majorana-Weyl condition consecutively in that order(which can only be done where d mod 8 = 2). Therefore, $\mathcal{N}=1$ SYM in ten dimensions has 16 components (real !) 

A Majorana spinor in four dimensions has 4 components. So, suppose you want 
$\mathcal{N}=4$ SYM in four dimensions (which has 16 [four copies of four components) you want to start with $\mathcal{N}=1$ SYM in ten dimensions. 

$\mathcal{N}=1$ SYM in four dimensions similarly has 4 components. So, if I want to construct a supersymmetric theory in two dimensions with four supercharges i.e $\mathcal{N}$ = (2,2) SYM (which has single component after imposing Majorana-Weyl), then one should start from $\mathcal{N}=1$ SYM in four dimensions and not with $\mathcal{N}=4$ SYM. 

16 supercharges:  
D=10, $\mathcal{N}$ = 1 $~\to~$ D=6, $\mathcal{N}$ = 2 $~\to~$ D=4, $\mathcal{N}$ = 4 $~\to~$ D=3, $\mathcal{N}$ = 8  $~\to~$ D=2, $\mathcal{N} = (8,8)$ 

8 supercharges:               
$\hspace{33mm}$ D=6, $\mathcal{N}$ = 1 $~\to~$ D=4, $\mathcal{N}$ = 2 $~\to~$ D=3, $\mathcal{N}$ = 4 

4 supercharges:            
$\hspace{64mm}$               D=4, $\mathcal{N}$ = 1 $~\to~$ D=3, $\mathcal{N}$ = 2