You can find an extensive combo list HEREBut the main combos I use are
c.LK,c.LP,c.HP xx Tatsu
Solar Plexus Strike,c.HP,Shoryuken(FADC to Ultra 1 if desired.)
(corner only)Solar Plexus Strike,c.HP,EX Tatsu,Ultra 1.
c.MK,EX Fireball,Ultra 1. Have to FADC the fireball if you arent in the corner.
Combos are important,because you need to maximiz your damage at every oppurtunity,but dont neglect learning footsies and zoning,those are your best friends as a ryu player.
Well there is a guide of sorts that can teach about footsies,I will link it at the end.However,a lot of footsies and zoning comes from experience and experimentation in the training room.You have to learn each characters pokes and tools,and what you have in your arsenal to deal with them.If a particular poke is giving you trouble you can just go to training and record the dummy doing it to see what beats it at what distance ect…As for zoning it is a matter of learning what your opponent can do to get past your fireballs,and knowing where you are safe when throwing a fireball,where you will be able to anti-air them after throwing a fireball if they jump it,also fireball should be thought of as a poke as well,you can win footsies with fireballs that are much harder otherwise.Throwing a fireball just outside of your opponents poke range can result in free damage and is near impossible to react to.Getting your anti-airs down is also very important.There should be a list of anti-airs where I linked you the combos.