For each case you pick the alg that suits you the most (aka fastest to execute)
Now, you're gonna want to use muscle memory instead of memorizing letter by letter (letter by letter is last resort tbh)
I memorize by looking at triggers, which are moves that can be done quickly. They're usually put in brackets to stand out within algs Some are:
sexy move (R U R' U') (R U R'), (R U2 R') etc are all pretty fast and easy to execute, there's also reverse sexy (U R U' R')
sledgehammer (R' F R F')
For example, OLL 27 (Sune) can be split into two triggers with a U turn ion between: (R U R') U (R U2 R') The first trigger is commonly used in F2L so you'll recognize it. The second is also used in F2L. Therefore, just memorize the two triggers and the order that they come in. Don't forget the U move in between.
OLL 24 is even easier: (r U R' U') (r' F R F'). It is basically a modified sexy move followed by a modified sledgehammer. Should be well in your muscle (memory) after you've executed the alg a few times.
For 2-look PLL it's basically the same thing but a bit more difficult as the algs are longer and less fingertricky.
Good luck and ask for clarification if this is unclear because I kinda rushed it.