I am very weak at RC. I am solving 12 RCs every day to increase my accuracy but then also my striking rate for solving the RC is from 20 % to 80%.

As the variation of accuracy rate is 20% to 80% - see what are the kind of passages where its 20% and where its 80%. Or what kind of question is troubling you - main point, inference, structure/organization.

12 RC's everyday !! - From where are you getting so may RC passage. Are they LSAT sets ?

The time taken is from 5 mins ( short passage) to 13 mins (if the passage seems to go over my head).

Refer all OG and VR passage and see :

1. What kind of templates usually occur in RC ( MGMAT RC gives you some good templates)
2. What are the general things to look for while reading the passage,working best for you.
3. Are GMAT biased ? - yes it is. For example in any "woman" or "minority" related topic, GMAT never seems to criticize them ( it always has a positive attitude towards woman and minorities). So obviously in main point/purpose passages you can eliminate all negative answer choices without even reading the passages.
4. What are the general trend of wrong answers - so that when you are lacking time, you can move on with educated guessing.
5. How "Inference questions" work. I generally find them to be the hardest of all other question types.
6. Have you ever came across any traditional conclusion in any passages ?
7. What are the structural differences between long and short passages - are they same ?

Work out for more of these kinds of traits, then automatically your timing and accuracy will improve.

In GMAT RC, passages going over the head is very uncommon - If you refer any VR and OG passages they are condensed but ordered in a structured way with a common theme, but not so hard that you couldn't decipher anything at one shot as that of Salman Rushdie's writing ( because both are meant for different audience). Questions are tough not because of the passage but because of the answer choices, its always the answer choices that makes the question tough and not the passages. (each passage has question from easy to hard )

My current RC strategy : Read the passage once thoroughly. Understand it.

Then solve the questions

a) For Main Idea & Inference question : By choosing the best answer among the options.
b) For Supporting the Ideas : Refer to passage if necessary

main ideas and Inference are different types : Broadly questions are categorized in three types :

1. Global question : main point, structure/organization,
2. specific types : inference, supporting facts, suggestion.
3. Concept based : parallelism, weaken/assumption/strengthen, principle questions

So each require different strategy :

here, for main point - go for prediction. Predict before reading the answer choice. In fact, for all global question predict and then move on with the answer choices.
For Inference - one have to refer the passage, find the relevant details and then play matching game. In Some inference, things won't be directly matching game but on how language works.

Keeping in view of all these, you can create your own strategy.

Here are some links that might help you :

https://www.beatthegmat.com/rc-logical-s ... tml#362906
https://www.beatthegmat.com/arsitoral-rc-t75750-15.html

Hope this helps !!