Either do cheat reps and focus on the negative (works with small exercise such as bicep curls) or drop set or super set.
My personal fav is the cheat and negative and I do it a lot for example in cable pulldown. Use a bit of bodyweight to pull it down and then 5s negative.
If you're looking at forced reps, you can do drop sets or add bands (assist rather than resist) to continue lifting for extra reps. For quicker drop sets, use some light plates (2.5# or 5#) which you can rapidly strip from the bar and continue a few reps.
For DB moves you can self-assist in some lifts using your other arm, or have lighter DBs to hand for additional reps.