Make sure
 

¿Aseguarse de algo, se usa el subjuntivo o no?

"I have to make sure there will be enough room in the suitcase."
"Tengo que asegurame de que hará o haya suficiente espacio en la maleta."

"You have to make sure that you get there on time."
"Tienes que asegurarte de que llegas o llegues a tiempo."

Subjunctive there, yes. :)

Both correct, different context.

If both are correct how do I know which to use? In the context here I was thinking of doing the suitcases and said ""I have to make sure there will be enough room in the suitcase." (To be able to buy some things in England and bring them back.)

Thanks for your help!

You use "haya" when you're just talking about your goal (having enough room in your suitcase). That supposes a simple action in the present or the future (just make sure there's enough room while you prepare the luggage). "Habrá" suggests there are actions or circumstances that may compromise that goal, so indicative somehow shows you prompt to take steps or further actions to make sure "que haya espacio".