Welcome.
MAD wrote
Any ideas what to do before applying to such position in order to guarantee it ?
Technically:
you have to check what programming language the company that you're interested in are using, for example (C++,C#,PHP..) but to be on the safe side i believe all companies requires OOP,HTML,CSS,JavaScript and probably JQuery.
so prepare yourself with these before the interview and you'll have a better chance.