There are a number of ways, hopefully as described below.
The 1st method is if the rootstock is approx twice the dia of the scion, and you can then use the ‘cleft graft’ as per fig 2 in http://www.ces.ncsu.edu/depts/hort/hil/grafting.html. You can do different cleft grafts on the same rootstock to suit the dia of the scions as per fig 1 in http://www.crfgsandiego.org/Documents/Grafting By Leo Manuel.pdf
The 2nd method is where the rootstock and scion can be approx the same dia, and you can do 2 ‘side grafts’ as in fig 5 in http://www.extension.umn.edu/distribution/horticulture/components/dg0532c.html . One above the other, by say 50mm but on opposite sides. See also fig 6b at www.nt.gov.au/d/Content/File/p/Tech_Bull/TB194.pdf Also sometimes called a ‘wedge graft’ as per http://www.hibiscusworld.com/graft/wedge.htm
A 3rd method is where the rootstock and scion can be approx the same dia, and you can do 2 ‘side veneer grafting’ as per fig 4 in http://www.ces.ncsu.edu/depts/hort/hil/grafting.html . One above the other, by say 50mm but on opposite sides.
A possible 4th method is via ‘spring budding’ (April) as per http://extension.missouri.edu/p/G6972 One above the other, by say 50mm but on opposite sides.
Another method that gives maximum cambium contact is via double whip and tongue grafting as per http://www.gb-online.co.uk/growing_guide/double%20whip%20and%20tongue001.pdf
I would probably plump for method 2 for a beginner, as being reasonably easy. But be aware that bending the rootstock to get the scion in, can sometimes snap the rootstock.