The best things to practice at the low level are footsies, spacing punish combos, and anti-airs. Anti-airs are huge. You can’t play the game really until the opponent knows he can’t just jump whenever he feels like it.
Combos to practice in SF4:
Cr.lk xx cr.lp, cr.hp xx hk tatsu
Cr.lk xx Cr.lp xx cr.lp, link hp srk. When you get this down, it leads into FADC ultra if you use lp SRK.
cr.lk xx cr.lp xx cr.lp, cr.hk - hard knockdown, very consistent, leads to Ryu’s hold up-forwards safe jump after sweep. (you literally just keep holding up forwards after the sweep, it’s a perfect frame safe jump on most characters).
cr.mp cr.mp cr.hk - cr.mp and cr.lp both allow the same combos afterwards. cr.lk xx cr.lp has similar pushback to one cr.mp however.
f.hp, cl.mk xx hp srk - it’s a 2 frame link, and it does almost the same damage as the one frame. You can FADC from cl.mk xx hadouken into cl.hp xx HP srk for a big 400 damage punish on uppercuts.
cr.hp xx hp SRK is a decent punish.
Ryu’s best anti-airs are really late MP SRK, cr.hp, far hk, and cr.mk.
Ryu’s best pokes are cr.mk, cr.mp, cr.hk (use sparingly), and far lp.
cr.lk xx s.lk, cr.lk xx mk pinwheel - reliable combo that works on most everyone, no hard links
cr.lk, cr.lk, cr.lk, cr.lk xx mk pinwheel - slightly harder combo off a chain.
s.mk xx fuhajin release, cr.mk xx pinwheel or cr.hk - Juri’s cl.mk is throw/low invincible like Rose’s and can be cancelled into her fireball for a combo. If they try to tech a throw when you do cl.mk, you will catch them with cl.mk.
cr.hp xx hk pinwheel is a good basic punish, or cr.mk xx hk pinwheel from farther away.
Far mp is her kara throw.
cr.mp is her best anti-air, cr.hp is slightly more greedy. j.mp is a good rising air to air.
Juri’s best pokes, as far as I know, are cr.mk, cr.hk, far hk, and far mp.
Juri might be easier when starting out because her anti-airs are normals, which are easier to time than anti-air uppercuts in SF4. And cr.mp is a REALLY good anti-air for some reason.