For me personally, I haven't tried to learn the formulae with mnemonics. Furthermore, I've only just started to use flashcards to learn them but only at times when my brain is most likely to remember them e.g. right before I go to sleep and then once again in the morning, I do use other methods alongside this.
Firstly before an exam, you could attempt lots of practise questions and always write down the formulas when you use them. Also, you could write them down and try to rearrange them to see which format you best remember them. (You could remember them best as formula triangles, words or by associating words with the symbols for the equation)
Last min tips (After you have done the tips above (flashcards etc..)) (DO NOT RELY ON THESE AS YOUR ONLY METHOD OF REVISION)
Right before an exam (for short term memory), you could keep writing down the formulas on a sheet of paper over and over again so when you get into the exam you can turn your paper to the back and write them all down whilst they're in your head. [This is what I try to do but do not rely on it if it's the only revision you will do!]
Whilst in an exam you may get a formula question where you are given some information such as the units for the answer. In most cases, the units are the formula! For example, the formula for density=mass/volume and the units are g/cm3 or kg/m3 (the / standing for divide if you use this technique).
Another thing in the exam, if you are really struggling to remember an equation, is that in most formulas for energy everything on the other side is multiplied. E.g. KE= 0.5 x m x v^2. And GPE= m x g x h. E=QV and E=Pt.
Finally, you will be given certain things to use in the question itself. Sometimes the question may be - State the formula linking density, mass and volume. (D=m/v) and then there will be a second question underneath asking you to work an answer out with given values. Tip: think about whether or not these values will have a positive relationship (One will increase as the other does [they will be timsed]) or whether they will have a negative relationship (One will decrease as the other does[they will be divided]). Lastly, does your answer seem reasonable? eg. would the weight of a truck on earth really be 10g? If not try another formula and check if your answer seems more accurate.
Hope this helps!