“Ang mga hilig ko” = My interests – “Mga hilig ko” is OK, but sounds rather crude.  It’s more standard to have an “ang” there.  “Hilig” is spelled with only one “L”.

“Ang isang hilig ko ay jiu jitsu.” = “Ang isa kong hilig ay jiu jitsu” = An interest of mine is jiu jitsu.

“Ang isa sa mga hilig ko ay jiu jitsu.” = One of my interests is jui jitsu.

“Gusto ko ang jiu jitsu kasi ito ay mabuti sa fitness at (nakakabawas ng) stress. = I like jiu jitsu because this is good for fitness and (reduces) stress.  - Wayne’s use of “kalusugan” is all right as maybe all of us might use that word when forced to translate “fitness”.  The word though means “health” in general.  I do not know what the Tagalog words for fitness and stress are because everyone here seems to just use the English words.  Some might write “istres”, but that would just be the Tagalog spelling of the English word.

“Gusto ko din ang mag-aral”.  = I also like studying/to study (referring to the act of stuying).  – You may also say “ang nag-aaral”, which would translate more to “learning” in this case.

“Gusto ko din mag-aral” = I also like to study (because I have not done so yet)

“Gusto ko din ang mag-aral upang/para matuto” = I also like to study in order to learn. – Just to show how “upang” is used, redundancy notwithstanding.  “Upang” is rarely used now though.  We use “para” instead.

Mag-aaral ako ng Tagalog, mathematics/matematika, at programming. = I will study Tagalog, mathematics, and programming.   – Some may use “pagpoprogram” instead of programming.)

Nag-aaral ako ng Tagalog.... = I am studying Tagalog....

“Hindi ako magaling/mahusay sa programming kasi beginner pa lang ako”. = I am not good in programming because I am still a beginner.  – “Mabuti” is “good”, but is used for describing character or to mean “beneficial”, as you correctly used for jiu jitsu earlier.  “Magaling” or “mahusay” means “good” when referring to skills. – Wayne correctly added the “lang” to mean “only/just”.  I added the “pa” to mean that your learning is in progress.  It would sound static without it.  For example, “nandito lang ako” would mean “I am just here (I am not moving from here)”, but “nandito pa lang ako” would mean, “I am still here (but will be moving on)”. 

On the use of “gusto”:

1.  You say “gusto ko ANG” when you are referring to a choice.  “Gusto ko ang jiu jitsu” would  mean that it is something that you like from other possible choices.

You say “gusto ko NG” when you want something and usually you want it at that moment.

“Gusto ko ANG kape” = I like coffee; I enjoy drinking coffee

“Gusto ko NG kape” = I want/would like to have coffee (now).

2. “Gusto” must and may only be followed by “ko”, “mo”, “niya”, “namin”, “ninyo”, or “nila”.   As a less popular alternative, it must and may be preceded exclusively by “aking”, “iyong”, “kaniyang”, “aming”, “inyong”, or “kanilang“.  You can’t use any other pronouns with it without attaching one of those mentioned that corresponds to the pronoun you want to use.  For example, if you would like to use “ako”, you can only do so by saying something like, “Ako, ang gusto ko ay ang mag-aral” or “Ako, ang aking gusto ay ang mag-aral”.   Therefore, “ako” is not really needed unless intended for emphasis.  To say, “Ako ang gusto ay ang mag-aral” would be along the line of saying, “Me Tarzan, you Jane”.  :-)  

Mga hillig ko

Green is for Grammer. You're sentences aren't too bad just keep in mind focus and non-focus when it comes to verbs and pronouns. 

Ang Isa kong hillig ay jiu jitsu. Gusto ko ang jiu jitsu kasi mabuti siya para sa kalusugan at stress ko. Gusto ko mag-aral ng Tagalog at mathematics at programming. Hindi ako magaling sa programming kasi nagsisimula  lang ako.

Mga hillig ko

or you can write it like this... :)

Mahilig akong mag Jiu Jitsu. Jiu jitsu ang gusto kasi mabuti ito sa fitness at sa stress. Gusto ko pang pag-aralan ito kagaya ng Tagalog, Matematika at Programming. Bahugan palang ako sa programming.

Mga hillig ko