The figures for twins differ widely, and depend on multiple factors. A safe figure as an AVERAGE only is about 1-3%.
On the MATERNAL side, a history of twins is significant, as it raises the likelihood of a repeat. This is believed to due to the woman having a genetic predisposition to hyperovulation (releasing more than one egg in some monthly cycles). If more than one egg is released, more than one egg can get fertilized, producing... twins!
Note that this only applies if the twins are fraternal (i.e. not identical). The process of making identical twins is completely different to making fraternal twins, and there is NO increased risk of identical twins recurring. [The odds are about 1:285]
The jury's still out on the risk if you have twins on the PATERNAL side - some studies suggest a mildly increased risk, others show no difference. Whatever the truth, any increased risk will be very small.
Note: the above image (Gemini) should not in any way be taken as an endorsement of the pile of crap that is astrology.