Clean the core properly using a q-tip dipped in some methyl hydrate (99% pure) allow a few seconds to dry. Using LOCTITE 401 (instant adhesive) squeeze two or so drops on the insert and spread around insert, then immediately press insert 'all the way' into the core of the arrow.
Make sure you get the insert all the way in on the first attempt, as this stuff bonds instantly--and you wouldn't want your insert stuck half-way into the arrow. You can then use an old rag and wipe the end of the insert removing whatever bit of glue was squeezed out.