Concentrated Action If you spend an action concentrating on a concentration spell (assuming no action is needed to use the spell). You get Advantage on your Concentration Roll.
Personalized Spells Casters may personalize their spells with minor alterations to the effect. This may grant some small role playing benefit (difficulty to recognize, surprise, bonus to intimidation, etc.) along with a compensating penalty (recognition, limited or delayed effects). Consult the DM with your suggestions. Learned spells (Warlocks, Wizards) require the caster learn each variation, granted spells (clerics, druids) may come “pre-personalized.”
Spells such as Charm Person, Detect Thoughts and others can be cast ‘subtly’. Doing so gives the target Advantage on saving throws, BUT, they don’t know that they’ve been affected by the spell.
Swapping Prepared Spells
Casters that prepare spells may swap up to half (round down) their spell casting class level in spells prepared with a short rest (this precludes any other short rest activities: healing, identifying magic items, etc..) So a 4th level caster can use a short rest to swap one or two prepared 1st or 2nd level spell(s) for another one or two 1st or 2nd level spells. This can’t change the number of spells a caster can have prepared at one time. Once a caster has done this, she cannot do it again until after a long rest.
All spells in the Player’s Handbook, those below, and those in the Temple of Elemental Evil player’s companion with DM’s approval.