can you describe a lucid dream that you have had to me, and from there i can be of more help.
But, most of the time, people who do gain lucidity lose it right away or wake up very soon after due to excitment. This will cause your blood to pump faster reaslies a whole bunch of chemicals in your brain and increase your wave lengths. Ultimitly you will awake from this, so the best thing to do, is to remain calm.
holding onto grass 
i used to do that too a long time ago. didnt help me much either.
Here are a few things that i would suggest you try next time you are inside a lucid dream. Remembering that each event and style is different from everyone. So choose the ones that you feel most comfortable with.
1.Remain calm ! ~~~~ its hard to start with but the more lucid dreams you have no matter how short the better you are going to get at it. So when you do wake up, dont get angry or upset, just breath smile to your self that you were lucid and renforce your self that next time you lucid dream it will last longer.
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Grab hold of something solid ~~~ this is a mind trick, which you have already tried, but instead of grass grab something more solid, Grass never worked for me, but a metal poll did. And as you grab it say to your self, stay here remain in the dream. or anyhting else you like.
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entice your senses.~~~~ mose of the time you will lose a dream from excitment etc etc, and as you do you will notice things start to fade, vision, hearing touch smell and as each of these fades you are going to find your self in either the black void for abit or awake now focusing on your awake senses. So instead while you are in the lucid dream focus on your dream senses. Grab a hand full of dirt, and feel it run thorugh your hands, toucha tree what does the bark feel like. Smell a flower or drink or eat something. Look around and experience your dream world.
I have found most of the time, my most powerful and longest lasting lucids have been when i have been compeatly involved in what i am doing inside the dream.
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screaming inside your dream.~ some people claim this works for them, it just blows up my dream.
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give your mind orders~ increase lucidity now works and only works if you mean it. Much like a RT.
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Do reality Tests ~~~ yes they help they reinforce that you are dreaming.
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Get moving. the more you move the more you are focusing on your dream enviroment, feel everything.
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Take it easy at the same time ~~~ dont always fight things or fly everywhere or have a heap of action. Look back over your longest lasting dreams you will find they have long periods of action and then rest then action action action then wake. or how ever you work.
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Try lucid dreaming early in the morning, Rem periods are longer then and you are more likely to catch a long and full rem period using wild then, then a crap 5 minute rem at the start of your period.
there is a link on the forum that will descirbe these techniques and may more. https://community.ld4all.com/t/prolonging-lucid-dreams/24077
this is one of them but there are many more too around the forum
good luck keep me upto date 