Es muy sencillo, solo tienes que asegurarte que la oracion sea en presente y que el verbo termine en ING. 

1.- I'm working on my English homework. 
2.- She's reading the newest Jane Green book. 
3.- They are watching a movie. 
4.- We are going to the park to feed the ducks. 
5.- You're talking too fast. 
6.- I'm waiting for a friend to arrive. 
7.- Ana is washing the dishes. 
8.- He is talking on the phone with his girlfriend. 
9.- They're mailing a birthday present to Rosy. 
10.- We're learning about present continuous. 
11.- The teacher is writing the exercise on the blackboard. 
12.- They're running a marathon. 
13.- My sister is baking a cake for her boyfriend. 
14.- David is cleaning the inside of his car. 
15.- He's packing what he needs for his travels.
16.-I am taking a nap.
17.-He is walking to the store.
18.-she is sleeping in her room.
19.-I am singing right now.
20.-We are writing a book.
21.-we aren't doing anything.
22.-he is kissing her.
23.- they're jumping rope at school.
24.-Valentina is meeting the boys
25.-She is singing and dancing at the concert
26.-We're seeing whats going around
27.-The man is looking at me.
28.-She is reading a book.
29.-We are looking at the people.
30.-I am showering ,tonight.
31.-i am writing this sentence.
32.-Bob is cleaning his computer.
33.-She is trying to win some tickets
34.-the fire fighter is turning off the fire.
35.-My dad is punishing me.
36.-My sister is bothering me.
37.-i am going to your house.
38.-We aren't typing tonight.
39.-She is going crazy
40.-We're doing our homework.

Lo resto hacelo vos;)