(Some extra advice) A para should be long but should be worth it! because if you write non-sense, it will be a waste of time to write it, as well as to read it! If you think that your para is relate able, it has good facts , and has a good content, then even if then para is short it doesn't matter. What matters the most is the content, the heart of your para. If you don't start the beginning good enough it will not be a good match with a very good content because, it will not make sense at all, if you start with a bad beginning and write a content that is way much better than it.

the way to write a para:
1)start with a beginning that makes sense and matches with your content(especially in stories, the plot should be relate able from the beginning till the end) for example:(it should not be like this at all)  the dog barked at Ramesh. Ramesh was in his school and went to the bathroom to take bath.
(how it should be) The dog barked on Ramesh while he was going to his school, Ramesh started running for his life after a long chase he reached his school, after his school sessions we're over he went to his home and took a bath. 

2)Don't make grammatical mistakes especially while framing a sentence.
(don't) I knowing all my friends, they don't do cheat with me.
(do)I know my friends, they will never cheat on me!

3) read a good learn English in 30 days book. If you have any problem reading it ask your elders, teachers, or parents.

4) listen to what your teacher teaches you at class and always take a note on things that are important!