Which way is the best way to creating a simple programming language?
Unlike a majority of people I don't believe that creating a language is about using a compiler or interpreter. While you will most likely need a compiler or interpreter to implement your new language, they are tools just as is a pencil and paper. Don't start by using a tool and think you have accomplished something. It would be like using a wrench to make an engine that doesn't work, but you claim you made an engine because use used a wrench.
To create a good programming language you have to have goal for your language.
Since you mention programming language as opposed to some other type of language such as SQL, or a markup language such as HTML, I will take it that you want a Turing complete language.
Since most Turing complete languages support arithmetic I would start with a simple arithmetic expression language and build on that. There are a huge amount of examples of these on the Internet, but be fore warned that many have problems.
Next learn how to build Abstract Syntax Trees (AST) for arithmetic expressions. i.e.
3 + 2 * 6
+
/ \
3 *
/ \
2 6
Do not use a compiler to build the AST, but build them by hand in the language you are using to write your programming language. i.e. If you are using Java to create a C++ compiler, then create the AST using Java.
Then write an evaluator for the AST that will walk the tree.
Once you are able to correctly build an AST and evaluate then add the lexer/parser which translates human readable source code into an AST. This is were you will need to get a good compiler design book.
Now you can compile the AST into assembly or byte code or just continue using an evaluator.
From this point on you just add features to your language, again starting by with the AST and then modifying the parser and code generator if you implemented one.
How to create a simple (with room to expanding) programming language?
As I noted: start with an arithmetic evaluator and add language concepts one at a time. Since you are new at this, you may find that a concept you add is actually better as a composition of simpler concepts and that you should add one of the simpler concepts first before adding the other concept finally reaching the higher concept.
Because your question is so general I can't give more specific answers. I see that you already have a few close votes noting such.