writing

watashiwa nihonjin sukidesh sosite nihongo benkyo sitai.

--> Watashi wa nihonjin ga sukidesu. Soshite nihongo wo benkyou sitai desu. 

       (or: Watashi wa nihonjin ga sukide, nihongo wo benkyou sitai desu. 

imakara watashiwa internet de nihongo benkyosimasu.

tokidoki watashiwa Skype de rensyo simasu.

--> Watashi wa tokidoki Skype de renshuu simasu. 

watasiwa nihonho benkyosimasu sigasi tsukawa naikara wasuremasu demo gambarimasu.

--> (a bit more natural: Watashi wa nihongo wo benkyou shiteimasu. Shikashi tsukawanai kara wasurete shimai masu. Demo ganbari masu. 

Good luck to your study.