There is also mixed opinion on whether old spells or new spells, or even self-written spells are best. Just because a spell is old, does not mean it will work. However, just because you wrote it yourself does not ensure it will work either. Neo-Pagans (new-age types) tend to emphasize the benefits of writing or creating your own spells, while folk-magic practitioners (grass-roots, old-school sorts), tend to embrace the benefits of learning spells from the older ones, or, if that is not possible, from written accounts of the old-time ways. There is one thing both sides agree on: if you create your own spells, it's good to have a broad-based knowledge of the magical meanings and uses of herbs, roots, minerals, colors, seals, amulets, astrological symbols, and similar items. It is also advantageous to be practiced at written or oral spells, before embarking on a new route
Source:http://www.spelwerx.com