For summarizing written text, a PTE test taker faces three challenges: writing a compound-complex sentence to be able to meet the one-sentence criterion; using appropriate punctuation marks; beating the summary word requirement of 50-70 words. 

Here  are sample summaries that illustrate these errors: 

To increase production manufacturing companies use Just-in-Time method that  inables less time and productions costs, this production significantly decrease less raw supplies and only based on the  current costumers demand in the market.

Australian koala bears  are on the brink of  extinction, according to experts, in order to  search for koala bears, wildlife conservators use  detection canine units that use low frequency methods  in order  to locate koala bears  current species population in the area. Based on their findings, koala population has been significantly dwindling. 

To get around these issues I suggest you do the following:  write directly into the box, so you can see the word count; writing directly into the  box saves you time in that you are able to edit and rephrase your single-sentence summary;  get the gist while reading the passage (better to write the gist in the box as well); expand the gist into a paraphrase but keeping the key words in place (avoid a verbatim summary); finally, re-read your summary and check  grammar issues.

Moreover, there are other  errors that I occasionally notice: run-on (incomplete) sentences, dangling/misplaced modifiers, vague/unclear  reasoning, and falling short of the word count. 

An effective method to beat the word requirement in case you fall short is to “pad” the sentence with adverbs (words modifying verbs).  I suggest you  set the time  limit shorter, so that in real summary writing you will be able to spare minutes for revision.     

In essay writing, a common issue is how to get it started.  Here’s a tip: when faced by a blank page, get ideas from the essay prompt and do a concept map—break down the bigger topic into smaller, workable topics. Then, choose one that you know most about.  Write anything that comes to mind—it need not be a full paragraph right away. Just write anything to get it started. 

This is what’s called  “free writing”. It works all the time.