If you would like to get a little more serious about bowling, an entry level bowling balls is your best bet. There is no way that plastic can be competitive in todays game as a strike ball. Spares are made with plastic!
Usual suggestions are the tornado series, scout series, power grooves and hits, however the best ball I have seen for an entry level bowler in a while is the SLATE GARGOYLE.
It has a strong (and driller friendly) core with a mild urethane cover, suitable for superhigh rev players, or low speed players. Works wonders on dry lanes!
The best thing about it, is that even though im not an 'entry level' bowler, I still use one for its durability and hit on lightly oiled lanes. They are also not overpriced, expecially for the results.
Ultimately it is the bowler that bowls the scores, however a ball that allows increased entry angle to the pocket does help a great deal. Perhaps coaching should also be on the menu.
let me know if you need any more info!!
Thanks
Andrew Tonkin