Oracle Database Express Edition (XE)

With an XE limitation of 1GB for the PGA and SGA, how would one best preserve this limitation?
In other words, how would one minimise the PGA and SGA usage via ones interface with Oracle?

For instance, in a SQL query I was building I could either (The query has multiple aggregates on multiple tables in a 'one to many' join relationship):
1) Use WITH clauses
2) Use inline views
3) Use standard views
4) Use temporary tables
5) Maybe more possibilities

Without much of an insite into how Oracle 'works' it's difficult to gauge which of these is less 'resource hungry'.
Possibly there is a reference on how to use the PGA & SGA efficiently?
Or possibly a more definitive explanation on what's actually stored in these memory areas (rather than just 'prorgam' and 'system' data).

Regards all,