Hoy quiero ponerme una camiseta lisa.

The base verb is poner (to put), but when you talk about putting clothing on yourself, Spanish uses the reflexive form ponerse (literally “to put [something] on oneself”).

• poner = to put (something somewhere)
  
  • Pongo el libro en la mesa. – I put the book on the table.
• ponerse = to put something on yourself (clothes, accessories, etc.)
  
  • Me pongo una camiseta. – I put on a T‑shirt.

In ponerme, the -me is the reflexive pronoun for yo (I):
poner + me → ponerme = to put (something) on myself.

So Hoy quiero ponerme una camiseta lisa = “Today I want to put on a plain T‑shirt.”

In Spanish, with an infinitive (like poner) that depends on another verb (like quiero), the reflexive pronoun can go in two correct positions:

• Before the conjugated verb:
  
  • Me quiero poner una camiseta lisa.
• Attached to the infinitive:
  
  • Quiero ponerme una camiseta lisa.

Me poner is incorrect; the pronoun never goes between me and the unconjugated verb like that. It either goes right before the conjugated verb or stuck to the end of the infinitive/gerund/affirmative imperative.

No difference in meaning. Both mean “I want to put on…”. The choice is mostly about style and rhythm:

• Me quiero poner una camiseta lisa.
• Quiero ponerme una camiseta lisa.

Both are fully natural and equally common in everyday speech.

The most natural positions for hoy in this sentence are:

• Hoy quiero ponerme una camiseta lisa.
• Quiero ponerme una camiseta lisa hoy.

Quiero hoy ponerme… is possible but sounds more marked or formal; you might hear it for emphasis or in written style, but not as the neutral everyday order.

Spanish often places time adverbs like hoy either:

• at the very beginning of the sentence, or
• at the very end.

Liso / lisa literally means “smooth,” but with clothes it usually means:

• plain, without any pattern, print, or design.

So una camiseta lisa is:

• a plain T‑shirt
• no stripes, no checks, no graphic print – just one solid color (or at least no noticeable pattern).

Adjectives in Spanish agree in gender and number with the noun they describe.

• camiseta is feminine singular → la camiseta
• So the adjective must also be feminine singular → lisa

Examples:

• un pantalón liso (masculine singular)
• unas camisetas lisas (feminine plural)
• unos pantalones lisos (masculine plural)

You can say una camiseta simple, but it doesn’t mean exactly the same:

• camiseta lisa: focuses on the lack of pattern/print (plain surface).
• camiseta simple: more about being simple, not fancy, maybe basic or not special.

If you specifically mean “no pattern / no print,” lisa is the most standard word.

In Spain:

• camiseta = T‑shirt (usually short-sleeved, knit, like a regular tee)
• camisa = shirt (with a collar, buttons, more formal, typically woven fabric)

So una camiseta lisa is a plain T‑shirt, not a dress shirt.

In Spanish, singular countable nouns almost always need an article (un/una or el/la), even where English sometimes omits it.

• Quiero ponerme una camiseta. – literally “I want to put on a T‑shirt.”
• Saying Quiero ponerme camiseta sounds incomplete or foreign.

So una camiseta is the natural way to say “a T‑shirt” in this context.

It expresses a present desire that usually refers to the very near future:

• Hoy quiero ponerme una camiseta lisa.
  = Today, I feel like / I want to put on a plain T‑shirt (at some point today).

Spanish normally uses:

• querer + infinitive for desire/intention (I want to…), and
• ir a + infinitive (voy a ponerme…) for a plan or immediate future (I’m going to…).

In everyday speech, quiero can feel quite close to “I’m going to” if the intention is strong and immediate, but grammatically it’s still “I want to.”

They focus on different aspects:

• ponerse – the action of putting clothing on:
  • Me voy a poner una camiseta lisa. – I’m going to put on a plain T‑shirt.
• llevar – wearing or carrying something (the state, not the action):
  • Hoy llevo una camiseta lisa. – Today I’m wearing a plain T‑shirt.
• vestir – to dress/wear (more formal or specific):
  • Viste de negro. – He/She dresses in black.
  • Visto una camiseta negra. – I wear a black T‑shirt (less common than llevar in everyday speech).

In your sentence, we’re talking about the act of putting it on, so ponerse is the right verb.

Yes, that sentence is grammatically correct, but:

• Quiero hoy ponerme una camiseta lisa sounds a bit formal, poetic, or specially emphasized.
• The neutral, everyday versions are:
  • Hoy quiero ponerme una camiseta lisa.
  • Quiero ponerme una camiseta lisa hoy.

Here’s ponerse in the present tense, for the action “to put on (clothes)”:

• yo – me pongo
• tú – te pones
• él / ella / usted – se pone
• nosotros / nosotras – nos ponemos
• vosotros / vosotras (mainly Spain) – os ponéis
• ellos / ellas / ustedes – se ponen

With querer + infinitive, the infinitive changes the pronoun:

• Quiero ponerme… – I want to put on…
• Quieres ponerte… – You (tú) want to put on…
• Quiere ponerse… – He/She/You (usted) want(s) to put on…
• Queremos ponernos… – We want to put on…
• Queréis poneros… – You (vosotros) want to put on…
• Quieren ponerse… – They / You (ustedes) want to put on…