Have a look at 5/3/1 for athletes by Jim Wendler... Will up your strength while ensuring you are recovering enough for your Rugby specific training.
Bump this! Add in intervals or HIIT with certain metabolic constraints. I'm not sure how long running bouts are in rugby, but I'm going to assume similar to football. So, sprints, prowler, tire/sled drags for 10-45seconds with rest or active recovery at double work cycle length to keep intensity high, but allow for recovery (ie. 1:2 to 1:3 ratio).