To start Front end development, you just need some basic knowledge in HTML(HTML5), css(css3), javascript, jQuery. but to master it, you need to practice a lot in the above technologies. nowadays, you can see a new framework every day. so pick a framework/library in javascript like angularjs, react js. and master in it. so if you have very good knowledge in one framework, i think it won't be difficult to learn another one. also it is useful to understand some css frameworks like bootstrap or foundation. it is good to have some knowledge in css preprocessors like SASS,Stylus,LESS.
Try to do as much as hobby projects as you can. All the best.