I am new to conlanging, and would like to create a language which English speakers can easily learn. How would you suggest I go about optimizing it for English speakers? Which features should I choose to allow English speakers to learn it easily?
Be extremely analytic.
Definitely don't inflect nouns. Keep verb and pronoun inflections to a bare minimum, and rely on modal verbs and adpositions as much as you can in place of complicated syntax rules. English inflection is so degenerate that including more than three forms per verb will be hard for English speakers -- you have slightly more leeway with pronouns, which in English decline into five forms under three principal parts, but don't overdo it.
Keep the phonology to a subset of English's.
English has a lot of vowels, usually at least 10. While you probably shouldn't try to use all of them, keep to ones that are common in multiple dialects of English: /ə/, /ɪ/, and /ɑː/ for instance.
Avoid <r> entirely. You don't want to deal with differences between the English <r> and your conlang's and if it is the same as one possible English <r> then some other English dialects are going to run into problems with it.
Avoid intervocalic /VtV/. In American English, a regular sound change flaps /VtV/ to /VɾV/, but this is not so in all dialects, and thus may cause issues.
Start with "normal" English and restrict it by adding rules specifically crafted for certain communication situations - one widely used and successful example is the Aeronautical phraseology, which, despite the name is actually a controlled language.
The easiest sort of conlang for English speakers would be one where the grammar of English is maintained unchanged, and you just add or replace a bunch of vocabulary. If you add a lot of new vocabulary for new concepts you could consider it some kind of new dialect. If you replace existing vocabulary so that the existing concepts are referred to with new words, then that's a relexification.
One example is The Gostak:
Finally, here you are. At the delcot of tondam, where doshes deave. But the doshery lutt is crenned with glauds.
Glauds! How rorm it would be to pell back to the bewl and distunk them, distunk the whole delcot, let the drokes discren them.
But you are the gostak. The gostak distims the doshes. And no glaud will vorl them from you.
Well, obviously plain English is the simplest language to an English speaker. You can simplify it it even further by restricting the vocabulary and get at designs like Basic English. Or you can aim at people with low competences in language or reading, for German there is Leichte Sprache in this domain, I am not aware of a special English in that domain (but very close to that is Simple English Wikipedia, the term Special English itself was used for the controlled language used by Voice of America.