When it comes to enforcement the starting point is the principle of effectiveness of EU law which is guaranteed by Art. 19(2) TEU and is also contained in Art. 47 of the Charter of Fundamental Rights. However it is not the EU itself that specifies principles but instead this is something that is left up to the Member States.
National legal systems decide how rights under EU law are to be protected (Rewe-Zentralfinanz [1976]) and there is no obligation for them to come up with new remedies (Rewe-Handelsgesellschaft Nord [1981]; Unibet Ltd v Justitiekanslern [2007]) although we have seen that change over the years with decisions like the one in Francovich.
National autonomy in this area is still central but has been eroded over the years by a number of other principles that have been developed by the ECJ. Equivalence tells us that remedies and procedures that are normally available in respect of national law should also be available in respect of EU law. Meanwhile practical possibility notes that national rules and procedures should not make the enforcement of EU law practically impossible (Barra v Belgium [1988]).
Proportionality is a general principles of EU law but in this context means that any sanctions etc. should not be disproportionate to the offence (Sagulo, Brenca and Bakhouce [1977]). Adequacy is also important and supplements the idea of effectiveness. In Von Colson it was noted that “compensation must…be adequate in relation to the damage sustained”. This also applies in other areas as seen by the case of Heylens [1987].
The principle of effectiveness is also something that itself has been strengthened by the CJEU over the years by cases such as Factortame I [1990] (interim relief); Dekker [1990]; Emmott [1991]; Marshall II [1993] (statutory limits).
In the late 90s this push was reversed to some extent by decisions like Steenhorst-Neerings [1993] and ex parte Eunice Sutton [1997].
Overall the approach of the CJEU is dependent on the right that is being enforced and the remedy that is being sought. Unfortunately this also creates some uncertainty and puts pressure on national courts to tread the line between enforcing national procedures and giving effect to rights under EU law.