First create a dictionary containing in the index location of each item in the list (you state that all items are unique, hence no issue with duplicate keys).

Then use the dictionary to look up each item's index location which is average time complexity O(1).

my_list = ['ab', 'sd', 'ef', 'de']
d = {item: idx for idx, item in enumerate(my_list)}

items_to_find = ['sd', 'ef', 'sd']

>>> [d.get(item) for item in items_to_find]
[1, 2, 1]

You can use operator.itemgetter:

from operator import itemgetter 
a = [-2, 1, 5, 3, 8, 5, 6]
b = [1, 2, 5]
print(itemgetter(*b)(a))
# Result:
(1, 5, 5)

Or you can use numpy:

import numpy as np
a = np.array([-2, 1, 5, 3, 8, 5, 6])
b = [1, 2, 5]
print(list(a[b]))
# Result:
[1, 5, 5]

But really, your current solution is fine. It's probably the neatest out of all of them.

Sounds like a one-liner Python is able to do!

[i for i, j in enumerate(myList) if 'how' in j.lower() or 'what' in j.lower()]

N = []

for i in range(len(L)):

    if L[i] in R:
        N.append(i)

or avoid indexing by using enumerate

N = []

for i, l in enumerate(L):
    
    if l in R:
        N.append(i)

or with a generator

N = [i for i in range(len(L)) if L[i] in R]

or with arrays

import numpy as np

N=np.where(np.isin(L,R))

It seems that you're trying to find occurrences of a word inside a string: the re library has a function called finditer that is ideal for this purpose. We can use this along with a list comprehension to make a list of the indexes of a word:

>>> import re
>>> word = "foo"
>>> string = "Bar foo lorem foo ipsum"
>>> [x.start() for x in re.finditer(word, string)]
[4, 14]

This function will find matches even if the word is inside another, like this:

>>> [x.start() for x in re.finditer("foo", "Lorem ipsum foobar")]
[12]

If you don't want this, encase your word inside a regular expression like this:

[x.start() for x in re.finditer("\s+" + word + "\s+", string)]

You can use a list comprehension with enumerate:

indices = [i for i, x in enumerate(my_list) if x == "whatever"]

The iterator enumerate(my_list) yields pairs (index, item) for each item in the list. Using i, x as loop variable target unpacks these pairs into the index i and the list item x. We filter down to all x that match our criterion, and select the indices i of these elements.