Welcome to the forum, David.
"How to improve students' language skills? " This is not a question. As it is not in itself a complete sentence, it is not even a statement. Such constructions are frequently, and acceptably, used as titles for articles and books, but not as direct questions. They are sometimes so used by native speakers, and are readily understood, but I recommend that you do not use them.
They are fine as part of such constructions as "I dont know how to ...." and "I asked him how to ...".
The natural, 'correct' questions are, "How do I/we/you ....?", "How can I/you/we ...?", "Can you tell me how I/we ...?" etc.
- For Teachers