I found myself working on this same problem (for homework), and I think I've written a fairly detailed solution. So I will post it here, in case it is helpful to anyone else.
Let $\mathfrak{g}$ be a 1-dimensional Lie algebra, and let $\{E_1\}$ be a basis for $\mathfrak{g}$. Then for any two vector fields $X,Y\in\mathfrak{g}$, we have $X=aE_1$ and $Y=bE_1$, for some $a,b\in\mathbb{R}$. Thus, $[X,Y]=[aE_1,bE_1]=ab[E_1,E_1]=0$ for all $X,Y\in\mathfrak{g}$. Therefore, the only 1-dimensional Lie algebra is the trivial one. The map $\varphi:\mathfrak{g}\rightarrow\mathfrak{gl}(2,\mathbb{R})$ $\varphi:aE_1\mapsto \left(\begin{array}{ll} a&0\\ 0&0 \end{array}\right)$ is a Lie algebra homomorphism, since $\varphi([aE_1,bE_1])=\varphi(0)=\left(\begin{array}{ll} 0&0\\ 0&0 \end{array}\right)\mbox{, and}$ $[\varphi(aE_1),\varphi(bE_1)]=\left(\begin{array}{ll} a&0\\ 0&0 \end{array}\right)\left(\begin{array}{ll} b&0\\ 0&0 \end{array}\right)-\left(\begin{array}{ll} b&0\\ 0&0 \end{array}\right)\left(\begin{array}{ll} a&0\\ 0&0 \end{array}\right)$ $=\left(\begin{array}{ll} 0&0\\ 0&0 \end{array}\right).$ Thus, $\mathfrak{g}$ is isomorphic to the (abelian) Lie subalgebra $\varphi(\mathfrak{g})=\left\{\left(\begin{array}{ll} a&0\\ 0&0 \end{array}\right)\in\mathfrak{gl}(2,\mathbb{R}):a\in\mathbb{R}\right\}\subset\mathfrak{gl}(2,\mathbb{R}).$
Now let $\mathfrak{h}$ be a 2-dimensional Lie algebra, and let $\{E_1,E_2\}$ be a basis for $\mathfrak{h}$. Then for any two vector fields $X,Y\in\mathfrak{h}$, we have $X=aE_1+bE_2$ and $Y=cE_1+dE_2$, for some $a,b,c,d\in\mathbb{R}$. Thus, $\begin{array}{ll} [X,Y]&=[aE_1+bE_2,cE_1+dE_2]\\ &=a[E_1,cE_1+dE_2]+b[E_2,cE_1+dE_2]\\ &=ac[E_1,E_1]+ad[E_1,E_2]+bc[E_2,E_1]+bd[E_2,E_2]\\ &=(ad-bc)[E_1,E_2]. \end{array}$
If $[E_1,E_2]=0$, then we have the trivial 2-dimensional Lie algebra. The map $\varphi:\mathfrak{h}\rightarrow\mathfrak{gl}(2,\mathbb{R})$ $\varphi:aE_1+bE_2\mapsto \left(\begin{array}{ll} a&0\\ 0&b \end{array}\right)$ is a Lie algebra homomorphism, since $\varphi([aE_1+bE_2,cE_1+dE_2])=\varphi(0)=\left(\begin{array}{ll} 0&0\\ 0&0 \end{array}\right)\mbox{, and}$
$[\varphi(aE_1+bE_2),\varphi(cE_1+dE_2)]=\left(\begin{array}{ll} a&0\\ 0&b \end{array}\right)\left(\begin{array}{ll} c&0\\ 0&d \end{array}\right)-\left(\begin{array}{ll} c&0\\ 0&d \end{array}\right)\left(\begin{array}{ll} a&0\\ 0&b \end{array}\right)$ $=\left(\begin{array}{ll} 0&0\\ 0&0 \end{array}\right).$Furthermore, this map is faithful (injective). Thus, $\mathfrak{h}$ is isomorphic to the (abelian) Lie subalgebra $\varphi(\mathfrak{h})=\left\{\left(\begin{array}{ll} a&0\\ 0&b \end{array}\right)\in\mathfrak{gl}(2,\mathbb{R}):a,b\in\mathbb{R}\right\}\subset\mathfrak{gl}(2,\mathbb{R}).$
If $[E_1,E_2]\neq0$, then set $E_3=[E_1,E_2]$. Then for all $X,Y\in\mathfrak{h}$ we have $[X,Y]=\lambda E_3$ for some $\lambda\in\mathbb{R}$. In particular, for any $E_4\in\mathfrak{g}$ such that $E_4$ and $E_3$ are linearly independent, we have $[E_4,E_3]=\lambda_0 E_3$. Replacing $E_4$ with $1/\lambda_0 E_4$, we now have a basis $\{E_4, E_3\}$ for $\mathfrak{g}$ such that $[E_4, E_3]=E_3$. The map $\varphi:\mathfrak{h}\rightarrow\mathfrak{gl}(2,\mathbb{R})$ $\varphi:aE_4+bE_3\mapsto \left(\begin{array}{ll} a&b\\ 0&0 \end{array}\right)$ is a Lie algebra homomorphism, since $\varphi([aE_4+bE_3,cE_4+dE_3])=\varphi((ad-bc)E_3)=\left(\begin{array}{ll} 0&ad-bc\\ 0&0 \end{array}\right)\mbox{, and}$
$[\varphi(aE_4+bE_3),\varphi(cE_4+dE_3)]=\left(\begin{array}{ll} a&b\\ 0&0 \end{array}\right)\left(\begin{array}{ll} c&d\\ 0&0 \end{array}\right)-\left(\begin{array}{ll} c&d\\ 0&0 \end{array}\right)\left(\begin{array}{ll} a&b\\ 0&0 \end{array}\right)$ $=\left(\begin{array}{ll} 0&ad-bc\\ 0&0 \end{array}\right).$Furthermore, this map is faithful (injective). Thus, $\mathfrak{h}$ is isomorphic to the (non-abelian) Lie subalgebra $\varphi(\mathfrak{h})=\left\{\left(\begin{array}{ll} a&b\\ 0&0 \end{array}\right)\in\mathfrak{gl}(2,\mathbb{R}):a,b\in\mathbb{R}\right\}\subset\mathfrak{gl}(2,\mathbb{R}).$