Hello,
You can use this plugin: http://wrobot.eu/files/file/517-potion-of-luck/ , edit it with notepad and replace id by your id.
You can also use "My Macro" in advanced general settings.
Or, if you want add it in your fightclass, in "Spell Settings" use "Timer", activate "Not spell, is lua script" and use this code is spell name: http://wrobot.eu/forums/topic/1688-lua-and-multi-language-support/
ps: http://wrobot.eu/forums/topic/2351-use-potionbuffitem-periodically/